lavc: Add coded bitstream read/write support for H.264

(cherry picked from commit acf06f45441be24c5cbae0920579cd69427326a1)
(cherry picked from commit 768eb9182e94a94bc2ef46f565a0dac7afef3b57)
(cherry picked from commit e7f64191b27bcf37cbf7006606f0f439c6cdc24f)

1 files changed, 1010 insertions, 0 deletions

diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
new file mode 100644
index 0000000000..f03fd3ce72
--- /dev/null
+++ b/libavcodec/cbs_h2645.c
@@ -0,0 +1,1010 @@
+/*
+ * 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/attributes.h"
+#include "libavutil/avassert.h"
+
+#include "bytestream.h"
+#include "cbs.h"
+#include "cbs_internal.h"
+#include "cbs_h264.h"
+#include "golomb.h"
+#include "h264.h"
+#include "h264_sei.h"
+#include "h2645_parse.h"
+
+
+static int cbs_read_ue_golomb(CodedBitstreamContext *ctx, GetBitContext *gbc,
+                              const char *name, uint32_t *write_to,
+                              uint32_t range_min, uint32_t range_max)
+{
+    uint32_t value;
+    int position, i, j;
+    unsigned int k;
+    char bits[65];
+
+    position = get_bits_count(gbc);
+
+    for (i = 0; i < 32; i++) {
+        if (get_bits_left(gbc) < i + 1) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid ue-golomb code at "
+                   "%s: bitstream ended.\n", name);
+            return AVERROR_INVALIDDATA;
+        }
+        k = get_bits1(gbc);
+        bits[i] = k ? '1' : '0';
+        if (k)
+            break;
+    }
+    if (i >= 32) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid ue-golomb code at "
+               "%s: more than 31 zeroes.\n", name);
+        return AVERROR_INVALIDDATA;
+    }
+    value = 1;
+    for (j = 0; j < i; j++) {
+        k = get_bits1(gbc);
+        bits[i + j + 1] = k ? '1' : '0';
+        value = value << 1 | k;
+    }
+    bits[i + j + 1] = 0;
+    --value;
+
+    if (ctx->trace_enable)
+        ff_cbs_trace_syntax_element(ctx, position, name, bits, value);
+
+    if (value < range_min || value > range_max) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "%s out of range: "
+               "%"PRIu32", but must be in [%"PRIu32",%"PRIu32"].\n",
+               name, value, range_min, range_max);
+        return AVERROR_INVALIDDATA;
+    }
+
+    *write_to = value;
+    return 0;
+}
+
+static int cbs_read_se_golomb(CodedBitstreamContext *ctx, GetBitContext *gbc,
+                              const char *name, int32_t *write_to,
+                              int32_t range_min, int32_t range_max)
+{
+    int32_t value;
+    int position, i, j;
+    unsigned int k;
+    uint32_t v;
+    char bits[65];
+
+    position = get_bits_count(gbc);
+
+    for (i = 0; i < 32; i++) {
+        if (get_bits_left(gbc) < i + 1) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid se-golomb code at "
+                   "%s: bitstream ended.\n", name);
+            return AVERROR_INVALIDDATA;
+        }
+        k = get_bits1(gbc);
+        bits[i] = k ? '1' : '0';
+        if (k)
+            break;
+    }
+    if (i >= 32) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid se-golomb code at "
+               "%s: more than 31 zeroes.\n", name);
+        return AVERROR_INVALIDDATA;
+    }
+    v = 1;
+    for (j = 0; j < i; j++) {
+        k = get_bits1(gbc);
+        bits[i + j + 1] = k ? '1' : '0';
+        v = v << 1 | k;
+    }
+    bits[i + j + 1] = 0;
+    if (v & 1)
+        value = -(int32_t)(v / 2);
+    else
+        value = v / 2;
+
+    if (ctx->trace_enable)
+        ff_cbs_trace_syntax_element(ctx, position, name, bits, value);
+
+    if (value < range_min || value > range_max) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "%s out of range: "
+               "%"PRId32", but must be in [%"PRId32",%"PRId32"].\n",
+               name, value, range_min, range_max);
+        return AVERROR_INVALIDDATA;
+    }
+
+    *write_to = value;
+    return 0;
+}
+
+static int cbs_write_ue_golomb(CodedBitstreamContext *ctx, PutBitContext *pbc,
+                               const char *name, uint32_t value,
+                               uint32_t range_min, uint32_t range_max)
+{
+    int len;
+
+    if (value < range_min || value > range_max) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "%s out of range: "
+               "%"PRIu32", but must be in [%"PRIu32",%"PRIu32"].\n",
+               name, value, range_min, range_max);
+        return AVERROR_INVALIDDATA;
+    }
+    av_assert0(value != UINT32_MAX);
+
+    len = av_log2(value + 1);
+    if (put_bits_left(pbc) < 2 * len + 1)
+        return AVERROR(ENOSPC);
+
+    if (ctx->trace_enable) {
+        char bits[65];
+        int i;
+
+        for (i = 0; i < len; i++)
+            bits[i] = '0';
+        bits[len] = '1';
+        for (i = 0; i < len; i++)
+            bits[len + i + 1] = (value + 1) >> (len - i - 1) & 1 ? '1' : '0';
+        bits[len + len + 1] = 0;
+
+        ff_cbs_trace_syntax_element(ctx, put_bits_count(pbc), name, bits, value);
+    }
+
+    put_bits(pbc, len, 0);
+    if (len + 1 < 32)
+        put_bits(pbc, len + 1, value + 1);
+    else
+        put_bits32(pbc, value + 1);
+
+    return 0;
+}
+
+static int cbs_write_se_golomb(CodedBitstreamContext *ctx, PutBitContext *pbc,
+                               const char *name, int32_t value,
+                               int32_t range_min, int32_t range_max)
+{
+    int len;
+    uint32_t uvalue;
+
+    if (value < range_min || value > range_max) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "%s out of range: "
+               "%"PRId32", but must be in [%"PRId32",%"PRId32"].\n",
+               name, value, range_min, range_max);
+        return AVERROR_INVALIDDATA;
+    }
+    av_assert0(value != INT32_MIN);
+
+    if (value == 0)
+        uvalue = 0;
+    else if (value > 0)
+        uvalue = 2 * (uint32_t)value - 1;
+    else
+        uvalue = 2 * (uint32_t)-value;
+
+    len = av_log2(uvalue + 1);
+    if (put_bits_left(pbc) < 2 * len + 1)
+        return AVERROR(ENOSPC);
+
+    if (ctx->trace_enable) {
+        char bits[65];
+        int i;
+
+        for (i = 0; i < len; i++)
+            bits[i] = '0';
+        bits[len] = '1';
+        for (i = 0; i < len; i++)
+            bits[len + i + 1] = (uvalue + 1) >> (len - i - 1) & 1 ? '1' : '0';
+        bits[len + len + 1] = 0;
+
+        ff_cbs_trace_syntax_element(ctx, put_bits_count(pbc), name, bits, value);
+    }
+
+    put_bits(pbc, len, 0);
+    if (len + 1 < 32)
+        put_bits(pbc, len + 1, uvalue + 1);
+    else
+        put_bits32(pbc, uvalue + 1);
+
+    return 0;
+}
+
+#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_H264(rw, name) FUNC_NAME(rw, h264, name)
+
+
+#define READ
+#define READWRITE read
+#define RWContext GetBitContext
+
+#define xu(width, name, var, range_min, range_max) do { \
+        uint32_t value = range_min; \
+        CHECK(ff_cbs_read_unsigned(ctx, rw, width, #name, \
+                                   &value, range_min, range_max)); \
+        var = value; \
+    } while (0)
+#define xue(name, var, range_min, range_max) do { \
+        uint32_t value = range_min; \
+        CHECK(cbs_read_ue_golomb(ctx, rw, #name, \
+                                 &value, range_min, range_max)); \
+        var = value; \
+    } while (0)
+#define xse(name, var, range_min, range_max) do { \
+        int32_t value = range_min; \
+        CHECK(cbs_read_se_golomb(ctx, rw, #name, \
+                                 &value, range_min, range_max)); \
+        var = value; \
+    } while (0)
+
+
+#define u(width, name, range_min, range_max) \
+        xu(width, name, current->name, range_min, range_max)
+#define flag(name) u(1, name, 0, 1)
+#define ue(name, range_min, range_max) \
+        xue(name, current->name, range_min, range_max)
+#define se(name, range_min, range_max) \
+        xse(name, current->name, range_min, range_max)
+
+#define infer(name, value) do { \
+        current->name = value; \
+    } while (0)
+
+static int cbs_h2645_read_more_rbsp_data(GetBitContext *gbc)
+{
+    int bits_left = get_bits_left(gbc);
+    if (bits_left > 8)
+        return 1;
+    if (show_bits(gbc, bits_left) == 1 << (bits_left - 1))
+        return 0;
+    return 1;
+}
+
+#define more_rbsp_data(var) ((var) = cbs_h2645_read_more_rbsp_data(rw))
+
+#define byte_alignment(rw) (get_bits_count(rw) % 8)
+
+#define allocate(name, size) do { \
+        name = av_mallocz(size); \
+        if (!name) \
+            return AVERROR(ENOMEM); \
+    } while (0)
+
+#define FUNC(name) FUNC_H264(READWRITE, name)
+#include "cbs_h264_syntax_template.c"
+#undef FUNC
+
+#undef READ
+#undef READWRITE
+#undef RWContext
+#undef xu
+#undef xue
+#undef xse
+#undef u
+#undef flag
+#undef ue
+#undef se
+#undef infer
+#undef more_rbsp_data
+#undef byte_alignment
+#undef allocate
+
+
+#define WRITE
+#define READWRITE write
+#define RWContext PutBitContext
+
+#define xu(width, name, var, range_min, range_max) do { \
+        uint32_t value = var; \
+        CHECK(ff_cbs_write_unsigned(ctx, rw, width, #name, \
+                                    value, range_min, range_max)); \
+    } while (0)
+#define xue(name, var, range_min, range_max) do { \
+        uint32_t value = var; \
+        CHECK(cbs_write_ue_golomb(ctx, rw, #name, \
+                                  value, range_min, range_max)); \
+    } while (0)
+#define xse(name, var, range_min, range_max) do { \
+        int32_t value = var; \
+        CHECK(cbs_write_se_golomb(ctx, rw, #name, \
+                                  value, range_min, range_max)); \
+    } while (0)
+
+#define u(width, name, range_min, range_max) \
+        xu(width, name, current->name, range_min, range_max)
+#define flag(name) u(1, name, 0, 1)
+#define ue(name, range_min, range_max) \
+        xue(name, current->name, range_min, range_max)
+#define se(name, range_min, range_max) \
+        xse(name, current->name, range_min, range_max)
+
+#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)
+
+#define more_rbsp_data(var) (var)
+
+#define byte_alignment(rw) (put_bits_count(rw) % 8)
+
+#define allocate(name, size) do { \
+        if (!name) { \
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "%s must be set " \
+                   "for writing.\n", #name); \
+            return AVERROR_INVALIDDATA; \
+        } \
+    } while (0)
+
+#define FUNC(name) FUNC_H264(READWRITE, name)
+#include "cbs_h264_syntax_template.c"
+#undef FUNC
+
+#undef WRITE
+#undef READWRITE
+#undef RWContext
+#undef xu
+#undef xue
+#undef xse
+#undef u
+#undef flag
+#undef ue
+#undef se
+#undef infer
+#undef more_rbsp_data
+#undef byte_alignment
+#undef allocate
+
+
+static void cbs_h264_free_sei(H264RawSEI *sei)
+{
+    int i;
+    for (i = 0; i < sei->payload_count; i++) {
+        H264RawSEIPayload *payload = &sei->payload[i];
+
+        switch (payload->payload_type) {
+        case H264_SEI_TYPE_BUFFERING_PERIOD:
+        case H264_SEI_TYPE_PIC_TIMING:
+        case H264_SEI_TYPE_RECOVERY_POINT:
+        case H264_SEI_TYPE_DISPLAY_ORIENTATION:
+            break;
+        case H264_SEI_TYPE_USER_DATA_REGISTERED:
+            av_freep(&payload->payload.user_data_registered.data);
+            break;
+        case H264_SEI_TYPE_USER_DATA_UNREGISTERED:
+            av_freep(&payload->payload.user_data_unregistered.data);
+            break;
+        default:
+            av_freep(&payload->payload.other.data);
+            break;
+        }
+    }
+}
+
+static void cbs_h264_free_slice(H264RawSlice *slice)
+{
+    av_freep(&slice->data);
+}
+
+static void cbs_h264_free_nal_unit(CodedBitstreamUnit *unit)
+{
+    switch (unit->type) {
+    case H264_NAL_SEI:
+        cbs_h264_free_sei(unit->content);
+        break;
+    case H264_NAL_IDR_SLICE:
+    case H264_NAL_SLICE:
+        cbs_h264_free_slice(unit->content);
+        break;
+    }
+    av_freep(&unit->content);
+}
+
+static int cbs_h2645_fragment_add_nals(CodedBitstreamContext *ctx,
+                                       CodedBitstreamFragment *frag,
+                                       const H2645Packet *packet)
+{
+    int err, i;
+
+    for (i = 0; i < packet->nb_nals; i++) {
+        const H2645NAL *nal = &packet->nals[i];
+        size_t size = nal->size;
+        uint8_t *data;
+
+        // Remove trailing zeroes.
+        while (size > 0 && nal->data[size - 1] == 0)
+            --size;
+        av_assert0(size > 0);
+
+        data = av_malloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
+        if (!data)
+            return AVERROR(ENOMEM);
+        memcpy(data, nal->data, size);
+        memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
+
+        err = ff_cbs_insert_unit_data(ctx, frag, -1, nal->type,
+                                      data, size);
+        if (err < 0) {
+            av_freep(&data);
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+static int cbs_h2645_split_fragment(CodedBitstreamContext *ctx,
+                                    CodedBitstreamFragment *frag,
+                                    int header)
+{
+    enum AVCodecID codec_id = ctx->codec->codec_id;
+    CodedBitstreamH2645Context *priv = ctx->priv_data;
+    GetByteContext gbc;
+    int err;
+
+    av_assert0(frag->data && frag->nb_units == 0);
+    if (frag->data_size == 0)
+        return 0;
+
+    if (header && frag->data[0] && codec_id == AV_CODEC_ID_H264) {
+        // AVCC header.
+        size_t size, start, end;
+        int i, count, version;
+
+        priv->mp4 = 1;
+
+        bytestream2_init(&gbc, frag->data, frag->data_size);
+
+        if (bytestream2_get_bytes_left(&gbc) < 6)
+            return AVERROR_INVALIDDATA;
+
+        version = bytestream2_get_byte(&gbc);
+        if (version != 1) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid AVCC header: "
+                   "first byte %u.", version);
+            return AVERROR_INVALIDDATA;
+        }
+
+        bytestream2_skip(&gbc, 3);
+        priv->nal_length_size = (bytestream2_get_byte(&gbc) & 3) + 1;
+
+        // SPS array.
+        count = bytestream2_get_byte(&gbc) & 0x1f;
+        start = bytestream2_tell(&gbc);
+        for (i = 0; i < count; i++) {
+            if (bytestream2_get_bytes_left(&gbc) < 2 * (count - i))
+                return AVERROR_INVALIDDATA;
+            size = bytestream2_get_be16(&gbc);
+            if (bytestream2_get_bytes_left(&gbc) < size)
+                return AVERROR_INVALIDDATA;
+            bytestream2_skip(&gbc, size);
+        }
+        end = bytestream2_tell(&gbc);
+
+        err = ff_h2645_packet_split(&priv->read_packet,
+                                    frag->data + start, end - start,
+                                    ctx->log_ctx, 1, 2, AV_CODEC_ID_H264, 1);
+        if (err < 0) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Failed to split AVCC SPS array.\n");
+            return err;
+        }
+        err = cbs_h2645_fragment_add_nals(ctx, frag, &priv->read_packet);
+        if (err < 0)
+            return err;
+
+        // PPS array.
+        count = bytestream2_get_byte(&gbc);
+        start = bytestream2_tell(&gbc);
+        for (i = 0; i < count; i++) {
+            if (bytestream2_get_bytes_left(&gbc) < 2 * (count - i))
+                return AVERROR_INVALIDDATA;
+            size = bytestream2_get_be16(&gbc);
+            if (bytestream2_get_bytes_left(&gbc) < size)
+                return AVERROR_INVALIDDATA;
+            bytestream2_skip(&gbc, size);
+        }
+        end = bytestream2_tell(&gbc);
+
+        err = ff_h2645_packet_split(&priv->read_packet,
+                                    frag->data + start, end - start,
+                                    ctx->log_ctx, 1, 2, AV_CODEC_ID_H264, 1);
+        if (err < 0) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Failed to split AVCC PPS array.\n");
+            return err;
+        }
+        err = cbs_h2645_fragment_add_nals(ctx, frag, &priv->read_packet);
+        if (err < 0)
+            return err;
+
+        if (bytestream2_get_bytes_left(&gbc) > 0) {
+            av_log(ctx->log_ctx, AV_LOG_WARNING, "%u bytes left at end of AVCC "
+                   "header.\n", bytestream2_get_bytes_left(&gbc));
+        }
+
+    } else {
+        // Annex B, or later MP4 with already-known parameters.
+
+        err = ff_h2645_packet_split(&priv->read_packet,
+                                    frag->data, frag->data_size,
+                                    ctx->log_ctx,
+                                    priv->mp4, priv->nal_length_size,
+                                    codec_id, 1);
+        if (err < 0)
+            return err;
+
+        err = cbs_h2645_fragment_add_nals(ctx, frag, &priv->read_packet);
+        if (err < 0)
+            return err;
+    }
+
+    return 0;
+}
+
+#define cbs_h2645_replace_ps(h26n, ps_name, ps_var, id_element) \
+static int cbs_h26 ## h26n ## _replace_ ## ps_var(CodedBitstreamContext *ctx, \
+                                                  const H26 ## h26n ## Raw ## ps_name *ps_var)  \
+{ \
+    CodedBitstreamH26 ## h26n ## Context *priv = ctx->priv_data; \
+    unsigned int id = ps_var->id_element; \
+    if (id > FF_ARRAY_ELEMS(priv->ps_var)) { \
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid " #ps_name \
+               " id : %d.\n", id); \
+        return AVERROR_INVALIDDATA; \
+    } \
+    av_freep(&priv->ps_var[id]); \
+    priv->ps_var[id] = av_malloc(sizeof(*ps_var)); \
+    if (!priv->ps_var[id]) \
+        return AVERROR(ENOMEM); \
+    memcpy(priv->ps_var[id], ps_var, sizeof(*ps_var)); \
+    return 0; \
+}
+
+cbs_h2645_replace_ps(4, SPS, sps, seq_parameter_set_id)
+cbs_h2645_replace_ps(4, PPS, pps, pic_parameter_set_id)
+
+static int cbs_h264_read_nal_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;
+
+    switch (unit->type) {
+    case H264_NAL_SPS:
+        {
+            H264RawSPS *sps;
+
+            sps = av_mallocz(sizeof(*sps));
+            if (!sps)
+                return AVERROR(ENOMEM);
+            err = cbs_h264_read_sps(ctx, &gbc, sps);
+            if (err >= 0)
+                err = cbs_h264_replace_sps(ctx, sps);
+            if (err < 0) {
+                av_free(sps);
+                return err;
+            }
+
+            unit->content = sps;
+        }
+        break;
+
+    case H264_NAL_SPS_EXT:
+        {
+            H264RawSPSExtension *sps_ext;
+
+            sps_ext = av_mallocz(sizeof(*sps_ext));
+            if (!sps_ext)
+                return AVERROR(ENOMEM);
+            err = cbs_h264_read_sps_extension(ctx, &gbc, sps_ext);
+            if (err < 0) {
+                av_free(sps_ext);
+                return err;
+            }
+
+            unit->content = sps_ext;
+        }
+        break;
+
+    case H264_NAL_PPS:
+        {
+            H264RawPPS *pps;
+
+            pps = av_mallocz(sizeof(*pps));
+            if (!pps)
+                return AVERROR(ENOMEM);
+            err = cbs_h264_read_pps(ctx, &gbc, pps);
+            if (err >= 0)
+                err = cbs_h264_replace_pps(ctx, pps);
+            if (err < 0) {
+                av_free(pps);
+                return err;
+            }
+
+            unit->content = pps;
+        }
+        break;
+
+    case H264_NAL_SLICE:
+    case H264_NAL_IDR_SLICE:
+    case H264_NAL_AUXILIARY_SLICE:
+        {
+            H264RawSlice *slice;
+            int pos, len;
+
+            slice = av_mallocz(sizeof(*slice));
+            if (!slice)
+                return AVERROR(ENOMEM);
+            err = cbs_h264_read_slice_header(ctx, &gbc, &slice->header);
+            if (err < 0) {
+                av_free(slice);
+                return err;
+            }
+
+            pos = get_bits_count(&gbc);
+            len = unit->data_size;
+            if (!unit->data[len - 1]) {
+                int z;
+                for (z = 0; z < len && !unit->data[len - z - 1]; z++);
+                av_log(ctx->log_ctx, AV_LOG_DEBUG, "Deleted %d trailing zeroes "
+                       "from slice data.\n", z);
+                len -= z;
+            }
+
+            slice->data_size = len - pos / 8;
+            slice->data = av_malloc(slice->data_size +
+                                    AV_INPUT_BUFFER_PADDING_SIZE);
+            if (!slice->data) {
+                av_free(slice);
+                return AVERROR(ENOMEM);
+            }
+            memcpy(slice->data,
+                   unit->data + pos / 8, slice->data_size);
+            memset(slice->data + slice->data_size, 0,
+                   AV_INPUT_BUFFER_PADDING_SIZE);
+            slice->data_bit_start = pos % 8;
+
+            unit->content = slice;
+        }
+        break;
+
+    case H264_NAL_AUD:
+        {
+            H264RawAUD *aud;
+
+            aud = av_mallocz(sizeof(*aud));
+            if (!aud)
+                return AVERROR(ENOMEM);
+            err = cbs_h264_read_aud(ctx, &gbc, aud);
+            if (err < 0) {
+                av_free(aud);
+                return err;
+            }
+
+            unit->content = aud;
+        }
+        break;
+
+    case H264_NAL_SEI:
+        {
+            H264RawSEI *sei;
+
+            sei = av_mallocz(sizeof(*sei));
+            if (!sei)
+                return AVERROR(ENOMEM);
+            err = cbs_h264_read_sei(ctx, &gbc, sei);
+            if (err < 0) {
+                cbs_h264_free_sei(sei);
+                return err;
+            }
+
+            unit->content = sei;
+        }
+        break;
+
+    default:
+        return AVERROR(ENOSYS);
+    }
+
+    return 0;
+}
+
+static int cbs_h264_write_nal_unit(CodedBitstreamContext *ctx,
+                                   CodedBitstreamUnit *unit,
+                                   PutBitContext *pbc)
+{
+    int err;
+
+    switch (unit->type) {
+    case H264_NAL_SPS:
+        {
+            H264RawSPS *sps = unit->content;
+
+            err = cbs_h264_write_sps(ctx, pbc, sps);
+            if (err < 0)
+                return err;
+
+            err = cbs_h264_replace_sps(ctx, sps);
+            if (err < 0)
+                return err;
+        }
+        break;
+
+    case H264_NAL_SPS_EXT:
+        {
+            H264RawSPSExtension *sps_ext;
+
+            err = cbs_h264_write_sps_extension(ctx, pbc, sps_ext);
+            if (err < 0)
+                return err;
+        }
+        break;
+
+    case H264_NAL_PPS:
+        {
+            H264RawPPS *pps = unit->content;
+
+            err = cbs_h264_write_pps(ctx, pbc, pps);
+            if (err < 0)
+                return err;
+
+            err = cbs_h264_replace_pps(ctx, pps);
+            if (err < 0)
+                return err;
+        }
+        break;
+
+    case H264_NAL_SLICE:
+    case H264_NAL_IDR_SLICE:
+        {
+            H264RawSlice *slice = unit->content;
+            GetBitContext gbc;
+            int bits_left, end, zeroes;
+
+            err = cbs_h264_write_slice_header(ctx, pbc, &slice->header);
+            if (err < 0)
+                return err;
+
+            if (slice->data) {
+                if (slice->data_size * 8 + 8 > put_bits_left(pbc))
+                    return AVERROR(ENOSPC);
+
+                init_get_bits(&gbc, slice->data, slice->data_size * 8);
+                skip_bits_long(&gbc, slice->data_bit_start);
+
+                // Copy in two-byte blocks, but stop before copying the
+                // rbsp_stop_one_bit in the final byte.
+                while (get_bits_left(&gbc) > 23)
+                    put_bits(pbc, 16, get_bits(&gbc, 16));
+
+                bits_left = get_bits_left(&gbc);
+                end = get_bits(&gbc, bits_left);
+
+                // rbsp_stop_one_bit must be present here.
+                av_assert0(end);
+                zeroes = ff_ctz(end);
+                if (bits_left > zeroes + 1)
+                    put_bits(pbc, bits_left - zeroes - 1,
+                             end >> (zeroes + 1));
+                put_bits(pbc, 1, 1);
+                while (put_bits_count(pbc) % 8 != 0)
+                    put_bits(pbc, 1, 0);
+            } else {
+                // No slice data - that was just the header.
+                // (Bitstream may be unaligned!)
+            }
+        }
+        break;
+
+    case H264_NAL_AUD:
+        {
+            err = cbs_h264_write_aud(ctx, pbc, unit->content);
+            if (err < 0)
+                return err;
+        }
+        break;
+
+    case H264_NAL_SEI:
+        {
+            err = cbs_h264_write_sei(ctx, pbc, unit->content);
+            if (err < 0)
+                return err;
+        }
+        break;
+
+    default:
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Write unimplemented for "
+               "NAL unit type %"PRIu32".\n", unit->type);
+        return AVERROR_PATCHWELCOME;
+    }
+
+    return 0;
+}
+
+static int cbs_h2645_write_nal_unit(CodedBitstreamContext *ctx,
+                                    CodedBitstreamUnit *unit)
+{
+    CodedBitstreamH2645Context *priv = ctx->priv_data;
+    enum AVCodecID codec_id = ctx->codec->codec_id;
+    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 "
+                   "%zu bytes).\n", priv->write_buffer_size);
+            return err;
+        }
+    }
+
+    init_put_bits(&pbc, priv->write_buffer, priv->write_buffer_size);
+
+    err = cbs_h264_write_nal_unit(ctx, unit, &pbc);
+
+    if (err == AVERROR(ENOSPC)) {
+        // Overflow.
+        priv->write_buffer_size *= 2;
+        goto reallocate_and_try_again;
+    }
+    // Overflow but we didn't notice.
+    av_assert0(put_bits_count(&pbc) <= 8 * priv->write_buffer_size);
+
+    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 = av_reallocp(&unit->data, unit->data_size);
+    if (err < 0)
+        return err;
+
+    memcpy(unit->data, priv->write_buffer, unit->data_size);
+
+    return 0;
+}
+
+static int cbs_h2645_assemble_fragment(CodedBitstreamContext *ctx,
+                                       CodedBitstreamFragment *frag)
+{
+    uint8_t *data;
+    size_t max_size, dp, sp;
+    int err, i, zero_run;
+
+    for (i = 0; i < frag->nb_units; i++) {
+        // Data should already all have been written when we get here.
+        av_assert0(frag->units[i].data);
+    }
+
+    max_size = 0;
+    for (i = 0; i < frag->nb_units; i++) {
+        // Start code + content with worst-case emulation prevention.
+        max_size += 3 + frag->units[i].data_size * 3 / 2;
+    }
+
+    data = av_malloc(max_size);
+    if (!data)
+        return AVERROR(ENOMEM);
+
+    dp = 0;
+    for (i = 0; i < frag->nb_units; i++) {
+        CodedBitstreamUnit *unit = &frag->units[i];
+
+        if (unit->data_bit_padding > 0) {
+            if (i < frag->nb_units - 1)
+                av_log(ctx->log_ctx, AV_LOG_WARNING, "Probably invalid "
+                       "unaligned padding on non-final NAL unit.\n");
+            else
+                frag->data_bit_padding = unit->data_bit_padding;
+        }
+
+        if (unit->type == H264_NAL_SPS ||
+            unit->type == H264_NAL_PPS ||
+            i == 0 /* (Assume this is the start of an access unit.) */) {
+            // zero_byte
+            data[dp++] = 0;
+        }
+        // start_code_prefix_one_3bytes
+        data[dp++] = 0;
+        data[dp++] = 0;
+        data[dp++] = 1;
+
+        zero_run = 0;
+        for (sp = 0; sp < unit->data_size; sp++) {
+            if (zero_run < 2) {
+                if (unit->data[sp] == 0)
+                    ++zero_run;
+                else
+                    zero_run = 0;
+            } else {
+                if ((unit->data[sp] & ~3) == 0) {
+                    // emulation_prevention_three_byte
+                    data[dp++] = 3;
+                }
+                zero_run = unit->data[sp] == 0;
+            }
+            data[dp++] = unit->data[sp];
+        }
+    }
+
+    av_assert0(dp <= max_size);
+    err = av_reallocp(&data, dp);
+    if (err)
+        return err;
+
+    frag->data = data;
+    frag->data_size = dp;
+
+    return 0;
+}
+
+static void cbs_h264_close(CodedBitstreamContext *ctx)
+{
+    CodedBitstreamH264Context *h264 = ctx->priv_data;
+    int i;
+
+    ff_h2645_packet_uninit(&h264->common.read_packet);
+
+    av_freep(&h264->common.write_buffer);
+
+    for (i = 0; i < FF_ARRAY_ELEMS(h264->sps); i++)
+        av_freep(&h264->sps[i]);
+    for (i = 0; i < FF_ARRAY_ELEMS(h264->pps); i++)
+        av_freep(&h264->pps[i]);
+}
+
+const CodedBitstreamType ff_cbs_type_h264 = {
+    .codec_id          = AV_CODEC_ID_H264,
+
+    .priv_data_size    = sizeof(CodedBitstreamH264Context),
+
+    .split_fragment    = &cbs_h2645_split_fragment,
+    .read_unit         = &cbs_h264_read_nal_unit,
+    .write_unit        = &cbs_h2645_write_nal_unit,
+    .assemble_fragment = &cbs_h2645_assemble_fragment,
+
+    .free_unit         = &cbs_h264_free_nal_unit,
+    .close             = &cbs_h264_close,
+};