libavcodec/cbs_mpeg2.c - 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 "internal.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 ui(width, name) \
         xui(width, name, current->name, 0, MAX_UINT_BITS(width), 0)
 #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 sis(width, name, subs, ...) \
         xsi(width, name, current->name, subs, __VA_ARGS__)


 #define READ
 #define READWRITE read
 #define RWContext GetBitContext

 #define xui(width, name, var, range_min, range_max, subs, ...) do { \
         uint32_t value = 0; \
         CHECK(ff_cbs_read_unsigned(ctx, rw, width, #name, \
                                    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 marker_bit() do { \
         av_unused uint32_t one; \
         CHECK(ff_cbs_read_unsigned(ctx, rw, 1, "marker_bit", NULL, &one, 1, 1)); \
     } while (0)

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

 #include "cbs_mpeg2_syntax_template.c"

 #undef READ
 #undef READWRITE
 #undef RWContext
 #undef xui
 #undef xsi
 #undef marker_bit
 #undef nextbits


 #define WRITE
 #define READWRITE write
 #define RWContext PutBitContext

 #define xui(width, name, var, range_min, range_max, subs, ...) do { \
         CHECK(ff_cbs_write_unsigned(ctx, rw, width, #name, \
                                     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 marker_bit() do { \
         CHECK(ff_cbs_write_unsigned(ctx, rw, 1, "marker_bit", NULL, 1, 1, 1)); \
     } while (0)

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

 #include "cbs_mpeg2_syntax_template.c"

 #undef WRITE
 #undef READWRITE
 #undef RWContext
 #undef xui
 #undef xsi
 #undef marker_bit
 #undef nextbits


 static void cbs_mpeg2_free_user_data(void *unit, uint8_t *content)
 {
     MPEG2RawUserData *user = (MPEG2RawUserData*)content;
     av_buffer_unref(&user->user_data_ref);
     av_freep(&content);
 }

 static void cbs_mpeg2_free_slice(void *unit, uint8_t *content)
 {
     MPEG2RawSlice *slice = (MPEG2RawSlice*)content;
     av_buffer_unref(&slice->header.extra_information_ref);
     av_buffer_unref(&slice->data_ref);
     av_freep(&content);
 }

 static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
                                     CodedBitstreamFragment *frag,
                                     int header)
 {
     const uint8_t *start, *end;
     uint8_t *unit_data;
     uint32_t start_code = -1, next_start_code = -1;
     size_t unit_size;
     int err, i, unit_type;

     start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,
                                    &start_code);
     for (i = 0;; i++) {
         end = avpriv_find_start_code(start, frag->data + frag->data_size,
                                      &next_start_code);

         unit_type = start_code & 0xff;

         // The start and end pointers point at to the byte following the
         // start_code_identifier in the start code that they found.
         if (end == frag->data + frag->data_size) {
             // We didn't find a start code, so this is the final unit.
             unit_size = end - (start - 1);
         } else {
             // Unit runs from start to the beginning of the start code
             // pointed to by end (including any padding zeroes).
             unit_size = (end - 4) - (start - 1);
         }

         unit_data = (uint8_t *)start - 1;

         err = ff_cbs_insert_unit_data(ctx, frag, i, unit_type,
                                       unit_data, unit_size, frag->data_ref);
         if (err < 0)
             return err;

         if (end == frag->data + frag->data_size)
             break;

         start_code = next_start_code;
         start = end;
     }

     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;

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

         err = ff_cbs_alloc_unit_content(ctx, unit, sizeof(*slice),
                                         &cbs_mpeg2_free_slice);
         if (err < 0)
             return err;
         slice = unit->content;

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

         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; \
                 err = ff_cbs_alloc_unit_content(ctx, unit, \
                                                 sizeof(*header), free_func); \
                 if (err < 0) \
                     return err; \
                 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,           NULL);
             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);
 #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);
 #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 &&
                    8 * slice->data_size > slice->data_bit_start);

         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)
 {
     CodedBitstreamMPEG2Context *priv = ctx->priv_data;
     PutBitContext pbc;
     int err;

     if (!priv->write_buffer) {
         // Initial write buffer size is 1MB.
         priv->write_buffer_size = 1024 * 1024;

     reallocate_and_try_again:
         err = av_reallocp(&priv->write_buffer, priv->write_buffer_size);
         if (err < 0) {
             av_log(ctx->log_ctx, AV_LOG_ERROR, "Unable to allocate a "
                    "sufficiently large write buffer (last attempt "
                    "%"SIZE_SPECIFIER" bytes).\n", priv->write_buffer_size);
             return err;
         }
     }

     init_put_bits(&pbc, priv->write_buffer, priv->write_buffer_size);

     if (MPEG2_START_IS_SLICE(unit->type))
         err = cbs_mpeg2_write_slice(ctx, unit, &pbc);
     else
         err = cbs_mpeg2_write_header(ctx, unit, &pbc);

     if (err == AVERROR(ENOSPC)) {
         // Overflow.
         priv->write_buffer_size *= 2;
         goto reallocate_and_try_again;
     }
     if (err < 0) {
         // Write failed for some other reason.
         return err;
     }

     if (put_bits_count(&pbc) % 8)
         unit->data_bit_padding = 8 - put_bits_count(&pbc) % 8;
     else
         unit->data_bit_padding = 0;

     unit->data_size = (put_bits_count(&pbc) + 7) / 8;
     flush_put_bits(&pbc);

     err = ff_cbs_alloc_unit_data(ctx, unit, unit->data_size);
     if (err < 0)
         return err;

     memcpy(unit->data, priv->write_buffer, unit->data_size);

     return 0;
 }

 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 void cbs_mpeg2_close(CodedBitstreamContext *ctx)
 {
     CodedBitstreamMPEG2Context *priv = ctx->priv_data;

     av_freep(&priv->write_buffer);
 }

 const CodedBitstreamType ff_cbs_type_mpeg2 = {
     .codec_id          = AV_CODEC_ID_MPEG2VIDEO,

     .priv_data_size    = sizeof(CodedBitstreamMPEG2Context),

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

     .close             = &cbs_mpeg2_close,
 };
	/*
	* 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 "internal.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 ui(width, name) \
	xui(width, name, current->name, 0, MAX_UINT_BITS(width), 0)
	#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 sis(width, name, subs, ...) \
	xsi(width, name, current->name, subs, __VA_ARGS__)


	#define READ
	#define READWRITE read
	#define RWContext GetBitContext

	#define xui(width, name, var, range_min, range_max, subs, ...) do { \
	uint32_t value = 0; \
	CHECK(ff_cbs_read_unsigned(ctx, rw, width, #name, \
	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 marker_bit() do { \
	av_unused uint32_t one; \
	CHECK(ff_cbs_read_unsigned(ctx, rw, 1, "marker_bit", NULL, &one, 1, 1)); \
	} while (0)

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

	#include "cbs_mpeg2_syntax_template.c"

	#undef READ
	#undef READWRITE
	#undef RWContext
	#undef xui
	#undef xsi
	#undef marker_bit
	#undef nextbits


	#define WRITE
	#define READWRITE write
	#define RWContext PutBitContext

	#define xui(width, name, var, range_min, range_max, subs, ...) do { \
	CHECK(ff_cbs_write_unsigned(ctx, rw, width, #name, \
	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 marker_bit() do { \
	CHECK(ff_cbs_write_unsigned(ctx, rw, 1, "marker_bit", NULL, 1, 1, 1)); \
	} while (0)

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

	#include "cbs_mpeg2_syntax_template.c"

	#undef WRITE
	#undef READWRITE
	#undef RWContext
	#undef xui
	#undef xsi
	#undef marker_bit
	#undef nextbits


	static void cbs_mpeg2_free_user_data(void unit, uint8_t content)
	{
	MPEG2RawUserData user = (MPEG2RawUserData)content;
	av_buffer_unref(&user->user_data_ref);
	av_freep(&content);
	}

	static void cbs_mpeg2_free_slice(void unit, uint8_t content)
	{
	MPEG2RawSlice slice = (MPEG2RawSlice)content;
	av_buffer_unref(&slice->header.extra_information_ref);
	av_buffer_unref(&slice->data_ref);
	av_freep(&content);
	}

	static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
	CodedBitstreamFragment *frag,
	int header)
	{
	const uint8_t start, end;
	uint8_t *unit_data;
	uint32_t start_code = -1, next_start_code = -1;
	size_t unit_size;
	int err, i, unit_type;

	start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,
	&start_code);
	for (i = 0;; i++) {
	end = avpriv_find_start_code(start, frag->data + frag->data_size,
	&next_start_code);

	unit_type = start_code & 0xff;

	// The start and end pointers point at to the byte following the
	// start_code_identifier in the start code that they found.
	if (end == frag->data + frag->data_size) {
	// We didn't find a start code, so this is the final unit.
	unit_size = end - (start - 1);
	} else {
	// Unit runs from start to the beginning of the start code
	// pointed to by end (including any padding zeroes).
	unit_size = (end - 4) - (start - 1);
	}

	unit_data = (uint8_t *)start - 1;

	err = ff_cbs_insert_unit_data(ctx, frag, i, unit_type,
	unit_data, unit_size, frag->data_ref);
	if (err < 0)
	return err;

	if (end == frag->data + frag->data_size)
	break;

	start_code = next_start_code;
	start = end;
	}

	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;

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

	err = ff_cbs_alloc_unit_content(ctx, unit, sizeof(*slice),
	&cbs_mpeg2_free_slice);
	if (err < 0)
	return err;
	slice = unit->content;

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

	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; \
	err = ff_cbs_alloc_unit_content(ctx, unit, \
	sizeof(*header), free_func); \
	if (err < 0) \
	return err; \
	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, NULL);
	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);
	#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);
	#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 &&
	8 * slice->data_size > slice->data_bit_start);

	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)
	{
	CodedBitstreamMPEG2Context *priv = ctx->priv_data;
	PutBitContext pbc;
	int err;

	if (!priv->write_buffer) {
	// Initial write buffer size is 1MB.
	priv->write_buffer_size = 1024 * 1024;

	reallocate_and_try_again:
	err = av_reallocp(&priv->write_buffer, priv->write_buffer_size);
	if (err < 0) {
	av_log(ctx->log_ctx, AV_LOG_ERROR, "Unable to allocate a "
	"sufficiently large write buffer (last attempt "
	"%"SIZE_SPECIFIER" bytes).\n", priv->write_buffer_size);
	return err;
	}
	}

	init_put_bits(&pbc, priv->write_buffer, priv->write_buffer_size);

	if (MPEG2_START_IS_SLICE(unit->type))
	err = cbs_mpeg2_write_slice(ctx, unit, &pbc);
	else
	err = cbs_mpeg2_write_header(ctx, unit, &pbc);

	if (err == AVERROR(ENOSPC)) {
	// Overflow.
	priv->write_buffer_size *= 2;
	goto reallocate_and_try_again;
	}
	if (err < 0) {
	// Write failed for some other reason.
	return err;
	}

	if (put_bits_count(&pbc) % 8)
	unit->data_bit_padding = 8 - put_bits_count(&pbc) % 8;
	else
	unit->data_bit_padding = 0;

	unit->data_size = (put_bits_count(&pbc) + 7) / 8;
	flush_put_bits(&pbc);

	err = ff_cbs_alloc_unit_data(ctx, unit, unit->data_size);
	if (err < 0)
	return err;

	memcpy(unit->data, priv->write_buffer, unit->data_size);

	return 0;
	}

	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 void cbs_mpeg2_close(CodedBitstreamContext *ctx)
	{
	CodedBitstreamMPEG2Context *priv = ctx->priv_data;

	av_freep(&priv->write_buffer);
	}

	const CodedBitstreamType ff_cbs_type_mpeg2 = {
	.codec_id = AV_CODEC_ID_MPEG2VIDEO,

	.priv_data_size = sizeof(CodedBitstreamMPEG2Context),

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

	.close = &cbs_mpeg2_close,
	};