libavcodec/cbs_mpeg2.c - play-games/ffmpeg - Git at Google


            
            /*

            
             * This file is part of FFmpeg.

            
             *

            
             * FFmpeg is free software; you can redistribute it and/or

            
             * modify it under the terms of the GNU Lesser General Public

            
             * License as published by the Free Software Foundation; either

            
             * version 2.1 of the License, or (at your option) any later version.

            
             *

            
             * FFmpeg is distributed in the hope that it will be useful,

            
             * but WITHOUT ANY WARRANTY; without even the implied warranty of

            
             * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

            
             * Lesser General Public License for more details.

            
             *

            
             * You should have received a copy of the GNU Lesser General Public

            
             * License along with FFmpeg; if not, write to the Free Software

            
             * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

            
             */


            #include "libavutil/avassert.h"


            #include "cbs.h"

            
            #include "cbs_internal.h"

            
            #include "cbs_mpeg2.h"

            
            #include "startcode.h"


            #define HEADER(name) do { \

            
                    ff_cbs_trace_header(ctx, name); \

            
                } while (0)


            #define CHECK(call) do { \

            
                    err = (call); \

            
                    if (err < 0) \

            
                        return err; \

            
                } while (0)


            #define FUNC_NAME(rw, codec, name) cbs_ ## codec ## _ ## rw ## _ ## name

            
            #define FUNC_MPEG2(rw, name) FUNC_NAME(rw, mpeg2, name)

            
            #define FUNC(name) FUNC_MPEG2(READWRITE, name)


            #define SUBSCRIPTS(subs, ...) (subs > 0 ? ((int[subs + 1]){ subs, __VA_ARGS__ }) : NULL)


            #define uir(width, name) \

            
                    xui(width, name, current->name, 1, MAX_UINT_BITS(width), 0, )

            
            #define uis(width, name, subs, ...) \

            
                    xui(width, name, current->name, 0, MAX_UINT_BITS(width), subs, __VA_ARGS__)

            
            #define uirs(width, name, subs, ...) \

            
                    xui(width, name, current->name, 1, MAX_UINT_BITS(width), subs, __VA_ARGS__)

            
            #define xui(width, name, var, range_min, range_max, subs, ...) \

            
                    xuia(width, #name, var, range_min, range_max, subs, __VA_ARGS__)

            
            #define sis(width, name, subs, ...) \

            
                    xsi(width, name, current->name, subs, __VA_ARGS__)


            #define marker_bit() \

            
                    bit("marker_bit", 1)

            
            #define bit(string, value) do { \

            
                    av_unused uint32_t bit = value; \

            
                    xuia(1, string, bit, value, value, 0, ); \

            
                } while (0)


            #define READ

            
            #define READWRITE read

            
            #define RWContext GetBitContext


            #define ui(width, name) do { \

            
                    uint32_t value; \

            
                    CHECK(ff_cbs_read_simple_unsigned(ctx, rw, width, #name, \

            
                                                      &value)); \

            
                    current->name = value; \

            
                } while (0)

            
            #define xuia(width, string, var, range_min, range_max, subs, ...) do { \

            
                    uint32_t value; \

            
                    CHECK(ff_cbs_read_unsigned(ctx, rw, width, string, \

            
                                               SUBSCRIPTS(subs, __VA_ARGS__), \

            
                                               &value, range_min, range_max)); \

            
                    var = value; \

            
                } while (0)


            #define xsi(width, name, var, subs, ...) do { \

            
                    int32_t value; \

            
                    CHECK(ff_cbs_read_signed(ctx, rw, width, #name, \

            
                                             SUBSCRIPTS(subs, __VA_ARGS__), &value, \

            
                                             MIN_INT_BITS(width), \

            
                                             MAX_INT_BITS(width))); \

            
                    var = value; \

            
                } while (0)


            #define nextbits(width, compare, var) \

            
                (get_bits_left(rw) >= width && \

            
                 (var = show_bits(rw, width)) == (compare))


            #define infer(name, value) do { \

            
                    current->name = value; \

            
                } while (0)


            #include "cbs_mpeg2_syntax_template.c"


            #undef READ

            
            #undef READWRITE

            
            #undef RWContext

            
            #undef ui

            
            #undef xuia

            
            #undef xsi

            
            #undef nextbits

            
            #undef infer


            #define WRITE

            
            #define READWRITE write

            
            #define RWContext PutBitContext


            #define ui(width, name) do { \

            
                    CHECK(ff_cbs_write_simple_unsigned(ctx, rw, width, #name, \

            
                                                       current->name)); \

            
                } while (0)


            #define xuia(width, string, var, range_min, range_max, subs, ...) do { \

            
                    CHECK(ff_cbs_write_unsigned(ctx, rw, width, string, \

            
                                                SUBSCRIPTS(subs, __VA_ARGS__), \

            
                                                var, range_min, range_max)); \

            
                } while (0)


            #define xsi(width, name, var, subs, ...) do { \

            
                    CHECK(ff_cbs_write_signed(ctx, rw, width, #name, \

            
                                              SUBSCRIPTS(subs, __VA_ARGS__), var, \

            
                                              MIN_INT_BITS(width), \

            
                                              MAX_INT_BITS(width))); \

            
                } while (0)


            #define nextbits(width, compare, var) (var)


            #define infer(name, value) do { \

            
                    if (current->name != (value)) { \

            
                        av_log(ctx->log_ctx, AV_LOG_WARNING, "Warning: " \

            
                               "%s does not match inferred value: " \

            
                               "%"PRId64", but should be %"PRId64".\n", \

            
                               #name, (int64_t)current->name, (int64_t)(value)); \

            
                    } \

            
                } while (0)


            #include "cbs_mpeg2_syntax_template.c"


            #undef WRITE

            
            #undef READWRITE

            
            #undef RWContext

            
            #undef ui

            
            #undef xuia

            
            #undef xsi

            
            #undef nextbits

            
            #undef infer


            static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,

            
                                                CodedBitstreamFragment *frag,

            
                                                int header)

            
            {

            
                const uint8_t *start;

            
                uint32_t start_code = -1;

            
                int err;


                start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,

            
                                               &start_code);

            
                if (start_code >> 8 != 0x000001) {

            
                    // No start code found.

            
                    return AVERROR_INVALIDDATA;

            
                }


                do {

            
                    CodedBitstreamUnitType unit_type = start_code & 0xff;

            
                    const uint8_t *end;

            
                    size_t unit_size;


                    // Reset start_code to ensure that avpriv_find_start_code()

            
                    // really reads a new start code and does not reuse the old

            
                    // start code in any way (as e.g. happens when there is a

            
                    // Sequence End unit at the very end of a packet).

            
                    start_code = UINT32_MAX;

            
                    end = avpriv_find_start_code(start--, frag->data + frag->data_size,

            
                                                 &start_code);


                    // start points to the byte containing the start_code_identifier

            
                    // (may be the last byte of fragment->data); end points to the byte

            
                    // following the byte containing the start code identifier (or to

            
                    // the end of fragment->data).

            
                    if (start_code >> 8 == 0x000001) {

            
                        // Unit runs from start to the beginning of the start code

            
                        // pointed to by end (including any padding zeroes).

            
                        unit_size = (end - 4) - start;

            
                    } else {

            
                       // We didn't find a start code, so this is the final unit.

            
                       unit_size = end - start;

            
                    }


                    err = ff_cbs_append_unit_data(frag, unit_type, (uint8_t*)start,

            
                                                  unit_size, frag->data_ref);

            
                    if (err < 0)

            
                        return err;


                    start = end;


                    // Do we have a further unit to add to the fragment?

            
                } while ((start_code >> 8) == 0x000001);


                return 0;

            
            }


            static int cbs_mpeg2_read_unit(CodedBitstreamContext *ctx,

            
                                           CodedBitstreamUnit *unit)

            
            {

            
                GetBitContext gbc;

            
                int err;


                err = init_get_bits(&gbc, unit->data, 8 * unit->data_size);

            
                if (err < 0)

            
                    return err;


                err = ff_cbs_alloc_unit_content(ctx, unit);

            
                if (err < 0)

            
                    return err;


                if (MPEG2_START_IS_SLICE(unit->type)) {

            
                    MPEG2RawSlice *slice = unit->content;

            
                    int pos, len;


                    err = cbs_mpeg2_read_slice_header(ctx, &gbc, &slice->header);

            
                    if (err < 0)

            
                        return err;


                    if (!get_bits_left(&gbc))

            
                        return AVERROR_INVALIDDATA;


                    pos = get_bits_count(&gbc);

            
                    len = unit->data_size;


                    slice->data_size = len - pos / 8;

            
                    slice->data_ref  = av_buffer_ref(unit->data_ref);

            
                    if (!slice->data_ref)

            
                        return AVERROR(ENOMEM);

            
                    slice->data = unit->data + pos / 8;


                    slice->data_bit_start = pos % 8;


                } else {

            
                    switch (unit->type) {

            
            #define START(start_code, type, read_func, free_func) \

            
                    case start_code: \

            
                        { \

            
                            type *header = unit->content; \

            
                            err = cbs_mpeg2_read_ ## read_func(ctx, &gbc, header); \

            
                            if (err < 0) \

            
                                return err; \

            
                        } \

            
                        break;

            
                        START(MPEG2_START_PICTURE,   MPEG2RawPictureHeader,

            
                              picture_header,           &cbs_mpeg2_free_picture_header);

            
                        START(MPEG2_START_USER_DATA, MPEG2RawUserData,

            
                              user_data,                &cbs_mpeg2_free_user_data);

            
                        START(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader,

            
                              sequence_header,          NULL);

            
                        START(MPEG2_START_EXTENSION, MPEG2RawExtensionData,

            
                              extension_data,           NULL);

            
                        START(MPEG2_START_GROUP,     MPEG2RawGroupOfPicturesHeader,

            
                              group_of_pictures_header, NULL);

            
                        START(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd,

            
                              sequence_end,             NULL);

            
            #undef START

            
                    default:

            
                        return AVERROR(ENOSYS);

            
                    }

            
                }


                return 0;

            
            }


            static int cbs_mpeg2_write_header(CodedBitstreamContext *ctx,

            
                                              CodedBitstreamUnit *unit,

            
                                              PutBitContext *pbc)

            
            {

            
                int err;


                switch (unit->type) {

            
            #define START(start_code, type, func) \

            
                case start_code: \

            
                    err = cbs_mpeg2_write_ ## func(ctx, pbc, unit->content); \

            
                    break;

            
                    START(MPEG2_START_PICTURE,         MPEG2RawPictureHeader,  picture_header);

            
                    START(MPEG2_START_USER_DATA,       MPEG2RawUserData,       user_data);

            
                    START(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader, sequence_header);

            
                    START(MPEG2_START_EXTENSION,       MPEG2RawExtensionData,  extension_data);

            
                    START(MPEG2_START_GROUP,           MPEG2RawGroupOfPicturesHeader,

            
                                                                     group_of_pictures_header);

            
                    START(MPEG2_START_SEQUENCE_END,    MPEG2RawSequenceEnd,    sequence_end);

            
            #undef START

            
                default:

            
                    av_log(ctx->log_ctx, AV_LOG_ERROR, "Write unimplemented for start "

            
                           "code %02"PRIx32".\n", unit->type);

            
                    return AVERROR_PATCHWELCOME;

            
                }


                return err;

            
            }


            static int cbs_mpeg2_write_slice(CodedBitstreamContext *ctx,

            
                                             CodedBitstreamUnit *unit,

            
                                             PutBitContext *pbc)

            
            {

            
                MPEG2RawSlice *slice = unit->content;

            
                int err;


                err = cbs_mpeg2_write_slice_header(ctx, pbc, &slice->header);

            
                if (err < 0)

            
                    return err;


                if (slice->data) {

            
                    size_t rest = slice->data_size - (slice->data_bit_start + 7) / 8;

            
                    uint8_t *pos = slice->data + slice->data_bit_start / 8;


                    av_assert0(slice->data_bit_start >= 0 &&

            
                               slice->data_size > slice->data_bit_start / 8);


                    if (slice->data_size * 8 + 8 > put_bits_left(pbc))

            
                        return AVERROR(ENOSPC);


                    // First copy the remaining bits of the first byte

            
                    if (slice->data_bit_start % 8)

            
                        put_bits(pbc, 8 - slice->data_bit_start % 8,

            
                                 *pos++ & MAX_UINT_BITS(8 - slice->data_bit_start % 8));


                    if (put_bits_count(pbc) % 8 == 0) {

            
                        // If the writer is aligned at this point,

            
                        // memcpy can be used to improve performance.

            
                        // This is the normal case.

            
                        flush_put_bits(pbc);

            
                        memcpy(put_bits_ptr(pbc), pos, rest);

            
                        skip_put_bytes(pbc, rest);

            
                    } else {

            
                        // If not, we have to copy manually:

            
                        for (; rest > 3; rest -= 4, pos += 4)

            
                            put_bits32(pbc, AV_RB32(pos));


                        for (; rest; rest--, pos++)

            
                            put_bits(pbc, 8, *pos);


                        // Align with zeros

            
                        put_bits(pbc, 8 - put_bits_count(pbc) % 8, 0);

            
                    }

            
                }


                return 0;

            
            }


            static int cbs_mpeg2_write_unit(CodedBitstreamContext *ctx,

            
                                            CodedBitstreamUnit *unit,

            
                                            PutBitContext *pbc)

            
            {

            
                if (MPEG2_START_IS_SLICE(unit->type))

            
                    return cbs_mpeg2_write_slice (ctx, unit, pbc);

            
                else

            
                    return cbs_mpeg2_write_header(ctx, unit, pbc);

            
            }


            static int cbs_mpeg2_assemble_fragment(CodedBitstreamContext *ctx,

            
                                                   CodedBitstreamFragment *frag)

            
            {

            
                uint8_t *data;

            
                size_t size, dp;

            
                int i;


                size = 0;

            
                for (i = 0; i < frag->nb_units; i++)

            
                    size += 3 + frag->units[i].data_size;


                frag->data_ref = av_buffer_alloc(size + AV_INPUT_BUFFER_PADDING_SIZE);

            
                if (!frag->data_ref)

            
                    return AVERROR(ENOMEM);

            
                data = frag->data_ref->data;


                dp = 0;

            
                for (i = 0; i < frag->nb_units; i++) {

            
                    CodedBitstreamUnit *unit = &frag->units[i];


                    data[dp++] = 0;

            
                    data[dp++] = 0;

            
                    data[dp++] = 1;


                    memcpy(data + dp, unit->data, unit->data_size);

            
                    dp += unit->data_size;

            
                }


                av_assert0(dp == size);


                memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);

            
                frag->data      = data;

            
                frag->data_size = size;


                return 0;

            
            }


            static const CodedBitstreamUnitTypeDescriptor cbs_mpeg2_unit_types[] = {

            
                CBS_UNIT_TYPE_INTERNAL_REF(MPEG2_START_PICTURE, MPEG2RawPictureHeader,

            
                                           extra_information_picture.extra_information),


                {

            
                    .nb_unit_types         = CBS_UNIT_TYPE_RANGE,

            
                    .unit_type.range.start = 0x01,

            
                    .unit_type.range.end   = 0xaf,


                    .content_type   = CBS_CONTENT_TYPE_INTERNAL_REFS,

            
                    .content_size   = sizeof(MPEG2RawSlice),

            
                    .type.ref = { .nb_offsets = 2,

            
                                  .offsets    = { offsetof(MPEG2RawSlice, header.extra_information_slice.extra_information),

            
                                                  offsetof(MPEG2RawSlice, data) } },

            
                },


                CBS_UNIT_TYPE_INTERNAL_REF(MPEG2_START_USER_DATA, MPEG2RawUserData,

            
                                           user_data),


                CBS_UNIT_TYPE_POD(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader),

            
                CBS_UNIT_TYPE_POD(MPEG2_START_EXTENSION,       MPEG2RawExtensionData),

            
                CBS_UNIT_TYPE_POD(MPEG2_START_SEQUENCE_END,    MPEG2RawSequenceEnd),

            
                CBS_UNIT_TYPE_POD(MPEG2_START_GROUP,           MPEG2RawGroupOfPicturesHeader),


                CBS_UNIT_TYPE_END_OF_LIST

            
            };


            const CodedBitstreamType ff_cbs_type_mpeg2 = {

            
                .codec_id          = AV_CODEC_ID_MPEG2VIDEO,


                .priv_data_size    = sizeof(CodedBitstreamMPEG2Context),


                .unit_types        = cbs_mpeg2_unit_types,


                .split_fragment    = &cbs_mpeg2_split_fragment,

            
                .read_unit         = &cbs_mpeg2_read_unit,

            
                .write_unit        = &cbs_mpeg2_write_unit,

            
                .assemble_fragment = &cbs_mpeg2_assemble_fragment,

            
            };
	/*
	* This file is part of FFmpeg.
	*
	* FFmpeg is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* FFmpeg is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with FFmpeg; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	*/

	#include "libavutil/avassert.h"

	#include "cbs.h"
	#include "cbs_internal.h"
	#include "cbs_mpeg2.h"
	#include "startcode.h"


	#define HEADER(name) do { \
	ff_cbs_trace_header(ctx, name); \
	} while (0)

	#define CHECK(call) do { \
	err = (call); \
	if (err < 0) \
	return err; \
	} while (0)

	#define FUNC_NAME(rw, codec, name) cbs_ ## codec ## _ ## rw ## _ ## name
	#define FUNC_MPEG2(rw, name) FUNC_NAME(rw, mpeg2, name)
	#define FUNC(name) FUNC_MPEG2(READWRITE, name)

	#define SUBSCRIPTS(subs, ...) (subs > 0 ? ((int[subs + 1]){ subs, __VA_ARGS__ }) : NULL)

	#define uir(width, name) \
	xui(width, name, current->name, 1, MAX_UINT_BITS(width), 0, )
	#define uis(width, name, subs, ...) \
	xui(width, name, current->name, 0, MAX_UINT_BITS(width), subs, __VA_ARGS__)
	#define uirs(width, name, subs, ...) \
	xui(width, name, current->name, 1, MAX_UINT_BITS(width), subs, __VA_ARGS__)
	#define xui(width, name, var, range_min, range_max, subs, ...) \
	xuia(width, #name, var, range_min, range_max, subs, __VA_ARGS__)
	#define sis(width, name, subs, ...) \
	xsi(width, name, current->name, subs, __VA_ARGS__)

	#define marker_bit() \
	bit("marker_bit", 1)
	#define bit(string, value) do { \
	av_unused uint32_t bit = value; \
	xuia(1, string, bit, value, value, 0, ); \
	} while (0)


	#define READ
	#define READWRITE read
	#define RWContext GetBitContext

	#define ui(width, name) do { \
	uint32_t value; \
	CHECK(ff_cbs_read_simple_unsigned(ctx, rw, width, #name, \
	&value)); \
	current->name = value; \
	} while (0)
	#define xuia(width, string, var, range_min, range_max, subs, ...) do { \
	uint32_t value; \
	CHECK(ff_cbs_read_unsigned(ctx, rw, width, string, \
	SUBSCRIPTS(subs, __VA_ARGS__), \
	&value, range_min, range_max)); \
	var = value; \
	} while (0)

	#define xsi(width, name, var, subs, ...) do { \
	int32_t value; \
	CHECK(ff_cbs_read_signed(ctx, rw, width, #name, \
	SUBSCRIPTS(subs, __VA_ARGS__), &value, \
	MIN_INT_BITS(width), \
	MAX_INT_BITS(width))); \
	var = value; \
	} while (0)

	#define nextbits(width, compare, var) \
	(get_bits_left(rw) >= width && \
	(var = show_bits(rw, width)) == (compare))

	#define infer(name, value) do { \
	current->name = value; \
	} while (0)

	#include "cbs_mpeg2_syntax_template.c"

	#undef READ
	#undef READWRITE
	#undef RWContext
	#undef ui
	#undef xuia
	#undef xsi
	#undef nextbits
	#undef infer


	#define WRITE
	#define READWRITE write
	#define RWContext PutBitContext

	#define ui(width, name) do { \
	CHECK(ff_cbs_write_simple_unsigned(ctx, rw, width, #name, \
	current->name)); \
	} while (0)

	#define xuia(width, string, var, range_min, range_max, subs, ...) do { \
	CHECK(ff_cbs_write_unsigned(ctx, rw, width, string, \
	SUBSCRIPTS(subs, __VA_ARGS__), \
	var, range_min, range_max)); \
	} while (0)

	#define xsi(width, name, var, subs, ...) do { \
	CHECK(ff_cbs_write_signed(ctx, rw, width, #name, \
	SUBSCRIPTS(subs, __VA_ARGS__), var, \
	MIN_INT_BITS(width), \
	MAX_INT_BITS(width))); \
	} while (0)

	#define nextbits(width, compare, var) (var)

	#define infer(name, value) do { \
	if (current->name != (value)) { \
	av_log(ctx->log_ctx, AV_LOG_WARNING, "Warning: " \
	"%s does not match inferred value: " \
	"%"PRId64", but should be %"PRId64".\n", \
	#name, (int64_t)current->name, (int64_t)(value)); \
	} \
	} while (0)

	#include "cbs_mpeg2_syntax_template.c"

	#undef WRITE
	#undef READWRITE
	#undef RWContext
	#undef ui
	#undef xuia
	#undef xsi
	#undef nextbits
	#undef infer


	static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
	CodedBitstreamFragment *frag,
	int header)
	{
	const uint8_t *start;
	uint32_t start_code = -1;
	int err;

	start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,
	&start_code);
	if (start_code >> 8 != 0x000001) {
	// No start code found.
	return AVERROR_INVALIDDATA;
	}

	do {
	CodedBitstreamUnitType unit_type = start_code & 0xff;
	const uint8_t *end;
	size_t unit_size;

	// Reset start_code to ensure that avpriv_find_start_code()
	// really reads a new start code and does not reuse the old
	// start code in any way (as e.g. happens when there is a
	// Sequence End unit at the very end of a packet).
	start_code = UINT32_MAX;
	end = avpriv_find_start_code(start--, frag->data + frag->data_size,
	&start_code);

	// start points to the byte containing the start_code_identifier
	// (may be the last byte of fragment->data); end points to the byte
	// following the byte containing the start code identifier (or to
	// the end of fragment->data).
	if (start_code >> 8 == 0x000001) {
	// Unit runs from start to the beginning of the start code
	// pointed to by end (including any padding zeroes).
	unit_size = (end - 4) - start;
	} else {
	// We didn't find a start code, so this is the final unit.
	unit_size = end - start;
	}

	err = ff_cbs_append_unit_data(frag, unit_type, (uint8_t*)start,
	unit_size, frag->data_ref);
	if (err < 0)
	return err;

	start = end;

	// Do we have a further unit to add to the fragment?
	} while ((start_code >> 8) == 0x000001);

	return 0;
	}

	static int cbs_mpeg2_read_unit(CodedBitstreamContext *ctx,
	CodedBitstreamUnit *unit)
	{
	GetBitContext gbc;
	int err;

	err = init_get_bits(&gbc, unit->data, 8 * unit->data_size);
	if (err < 0)
	return err;

	err = ff_cbs_alloc_unit_content(ctx, unit);
	if (err < 0)
	return err;

	if (MPEG2_START_IS_SLICE(unit->type)) {
	MPEG2RawSlice *slice = unit->content;
	int pos, len;

	err = cbs_mpeg2_read_slice_header(ctx, &gbc, &slice->header);
	if (err < 0)
	return err;

	if (!get_bits_left(&gbc))
	return AVERROR_INVALIDDATA;

	pos = get_bits_count(&gbc);
	len = unit->data_size;

	slice->data_size = len - pos / 8;
	slice->data_ref = av_buffer_ref(unit->data_ref);
	if (!slice->data_ref)
	return AVERROR(ENOMEM);
	slice->data = unit->data + pos / 8;

	slice->data_bit_start = pos % 8;

	} else {
	switch (unit->type) {
	#define START(start_code, type, read_func, free_func) \
	case start_code: \
	{ \
	type *header = unit->content; \
	err = cbs_mpeg2_read_ ## read_func(ctx, &gbc, header); \
	if (err < 0) \
	return err; \
	} \
	break;
	START(MPEG2_START_PICTURE, MPEG2RawPictureHeader,
	picture_header, &cbs_mpeg2_free_picture_header);
	START(MPEG2_START_USER_DATA, MPEG2RawUserData,
	user_data, &cbs_mpeg2_free_user_data);
	START(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader,
	sequence_header, NULL);
	START(MPEG2_START_EXTENSION, MPEG2RawExtensionData,
	extension_data, NULL);
	START(MPEG2_START_GROUP, MPEG2RawGroupOfPicturesHeader,
	group_of_pictures_header, NULL);
	START(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd,
	sequence_end, NULL);
	#undef START
	default:
	return AVERROR(ENOSYS);
	}
	}

	return 0;
	}

	static int cbs_mpeg2_write_header(CodedBitstreamContext *ctx,
	CodedBitstreamUnit *unit,
	PutBitContext *pbc)
	{
	int err;

	switch (unit->type) {
	#define START(start_code, type, func) \
	case start_code: \
	err = cbs_mpeg2_write_ ## func(ctx, pbc, unit->content); \
	break;
	START(MPEG2_START_PICTURE, MPEG2RawPictureHeader, picture_header);
	START(MPEG2_START_USER_DATA, MPEG2RawUserData, user_data);
	START(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader, sequence_header);
	START(MPEG2_START_EXTENSION, MPEG2RawExtensionData, extension_data);
	START(MPEG2_START_GROUP, MPEG2RawGroupOfPicturesHeader,
	group_of_pictures_header);
	START(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd, sequence_end);
	#undef START
	default:
	av_log(ctx->log_ctx, AV_LOG_ERROR, "Write unimplemented for start "
	"code %02"PRIx32".\n", unit->type);
	return AVERROR_PATCHWELCOME;
	}

	return err;
	}

	static int cbs_mpeg2_write_slice(CodedBitstreamContext *ctx,
	CodedBitstreamUnit *unit,
	PutBitContext *pbc)
	{
	MPEG2RawSlice *slice = unit->content;
	int err;

	err = cbs_mpeg2_write_slice_header(ctx, pbc, &slice->header);
	if (err < 0)
	return err;

	if (slice->data) {
	size_t rest = slice->data_size - (slice->data_bit_start + 7) / 8;
	uint8_t *pos = slice->data + slice->data_bit_start / 8;

	av_assert0(slice->data_bit_start >= 0 &&
	slice->data_size > slice->data_bit_start / 8);

	if (slice->data_size * 8 + 8 > put_bits_left(pbc))
	return AVERROR(ENOSPC);

	// First copy the remaining bits of the first byte
	if (slice->data_bit_start % 8)
	put_bits(pbc, 8 - slice->data_bit_start % 8,
	*pos++ & MAX_UINT_BITS(8 - slice->data_bit_start % 8));

	if (put_bits_count(pbc) % 8 == 0) {
	// If the writer is aligned at this point,
	// memcpy can be used to improve performance.
	// This is the normal case.
	flush_put_bits(pbc);
	memcpy(put_bits_ptr(pbc), pos, rest);
	skip_put_bytes(pbc, rest);
	} else {
	// If not, we have to copy manually:
	for (; rest > 3; rest -= 4, pos += 4)
	put_bits32(pbc, AV_RB32(pos));

	for (; rest; rest--, pos++)
	put_bits(pbc, 8, *pos);

	// Align with zeros
	put_bits(pbc, 8 - put_bits_count(pbc) % 8, 0);
	}
	}

	return 0;
	}

	static int cbs_mpeg2_write_unit(CodedBitstreamContext *ctx,
	CodedBitstreamUnit *unit,
	PutBitContext *pbc)
	{
	if (MPEG2_START_IS_SLICE(unit->type))
	return cbs_mpeg2_write_slice (ctx, unit, pbc);
	else
	return cbs_mpeg2_write_header(ctx, unit, pbc);
	}

	static int cbs_mpeg2_assemble_fragment(CodedBitstreamContext *ctx,
	CodedBitstreamFragment *frag)
	{
	uint8_t *data;
	size_t size, dp;
	int i;

	size = 0;
	for (i = 0; i < frag->nb_units; i++)
	size += 3 + frag->units[i].data_size;

	frag->data_ref = av_buffer_alloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
	if (!frag->data_ref)
	return AVERROR(ENOMEM);
	data = frag->data_ref->data;

	dp = 0;
	for (i = 0; i < frag->nb_units; i++) {
	CodedBitstreamUnit *unit = &frag->units[i];

	data[dp++] = 0;
	data[dp++] = 0;
	data[dp++] = 1;

	memcpy(data + dp, unit->data, unit->data_size);
	dp += unit->data_size;
	}

	av_assert0(dp == size);

	memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
	frag->data = data;
	frag->data_size = size;

	return 0;
	}

	static const CodedBitstreamUnitTypeDescriptor cbs_mpeg2_unit_types[] = {
	CBS_UNIT_TYPE_INTERNAL_REF(MPEG2_START_PICTURE, MPEG2RawPictureHeader,
	extra_information_picture.extra_information),

	{
	.nb_unit_types = CBS_UNIT_TYPE_RANGE,
	.unit_type.range.start = 0x01,
	.unit_type.range.end = 0xaf,

	.content_type = CBS_CONTENT_TYPE_INTERNAL_REFS,
	.content_size = sizeof(MPEG2RawSlice),
	.type.ref = { .nb_offsets = 2,
	.offsets = { offsetof(MPEG2RawSlice, header.extra_information_slice.extra_information),
	offsetof(MPEG2RawSlice, data) } },
	},

	CBS_UNIT_TYPE_INTERNAL_REF(MPEG2_START_USER_DATA, MPEG2RawUserData,
	user_data),

	CBS_UNIT_TYPE_POD(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader),
	CBS_UNIT_TYPE_POD(MPEG2_START_EXTENSION, MPEG2RawExtensionData),
	CBS_UNIT_TYPE_POD(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd),
	CBS_UNIT_TYPE_POD(MPEG2_START_GROUP, MPEG2RawGroupOfPicturesHeader),

	CBS_UNIT_TYPE_END_OF_LIST
	};

	const CodedBitstreamType ff_cbs_type_mpeg2 = {
	.codec_id = AV_CODEC_ID_MPEG2VIDEO,

	.priv_data_size = sizeof(CodedBitstreamMPEG2Context),

	.unit_types = cbs_mpeg2_unit_types,

	.split_fragment = &cbs_mpeg2_split_fragment,
	.read_unit = &cbs_mpeg2_read_unit,
	.write_unit = &cbs_mpeg2_write_unit,
	.assemble_fragment = &cbs_mpeg2_assemble_fragment,
	};