lavc: Add coded bitstream read/write API

(cherry picked from commit 18f1706f331bf5dd565774eae680508c8d3a97ad)
(cherry picked from commit 44cde38c8acbef7d5250e6d1b52b1020871e093b)

4 files changed, 877 insertions, 0 deletions

diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index c4ec09b1c4..9680553c90 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -59,6 +59,7 @@ OBJS-$(CONFIG_AUDIODSP)                += audiodsp.o
 OBJS-$(CONFIG_BLOCKDSP)                += blockdsp.o
 OBJS-$(CONFIG_BSWAPDSP)                += bswapdsp.o
 OBJS-$(CONFIG_CABAC)                   += cabac.o
+OBJS-$(CONFIG_CBS)                     += cbs.o
 OBJS-$(CONFIG_CRYSTALHD)               += crystalhd.o
 OBJS-$(CONFIG_DCT)                     += dct.o dct32_fixed.o dct32_float.o
 OBJS-$(CONFIG_ERROR_RESILIENCE)        += error_resilience.o
diff --git a/libavcodec/cbs.c b/libavcodec/cbs.c
new file mode 100644
index 0000000000..fa68040cfa
--- /dev/null
+++ b/libavcodec/cbs.c
@@ -0,0 +1,482 @@
+/*
+ * 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 <string.h>
+
+#include "config.h"
+
+#include "libavutil/avassert.h"
+#include "libavutil/common.h"
+
+#include "cbs.h"
+#include "cbs_internal.h"
+
+
+static const CodedBitstreamType *cbs_type_table[] = {
+};
+
+int ff_cbs_init(CodedBitstreamContext **ctx_ptr,
+                enum AVCodecID codec_id, void *log_ctx)
+{
+    CodedBitstreamContext *ctx;
+    const CodedBitstreamType *type;
+    int i;
+
+    type = NULL;
+    for (i = 0; i < FF_ARRAY_ELEMS(cbs_type_table); i++) {
+        if (cbs_type_table[i]->codec_id == codec_id) {
+            type = cbs_type_table[i];
+            break;
+        }
+    }
+    if (!type)
+        return AVERROR(EINVAL);
+
+    ctx = av_mallocz(sizeof(*ctx));
+    if (!ctx)
+        return AVERROR(ENOMEM);
+
+    ctx->log_ctx = log_ctx;
+    ctx->codec   = type;
+
+    ctx->priv_data = av_mallocz(ctx->codec->priv_data_size);
+    if (!ctx->priv_data) {
+        av_freep(&ctx);
+        return AVERROR(ENOMEM);
+    }
+
+    ctx->decompose_unit_types = NULL;
+
+    ctx->trace_enable = 0;
+    ctx->trace_level  = AV_LOG_TRACE;
+
+    *ctx_ptr = ctx;
+    return 0;
+}
+
+void ff_cbs_close(CodedBitstreamContext **ctx_ptr)
+{
+    CodedBitstreamContext *ctx = *ctx_ptr;
+
+    if (!ctx)
+        return;
+
+    if (ctx->codec && ctx->codec->close)
+        ctx->codec->close(ctx);
+
+    av_freep(&ctx->priv_data);
+    av_freep(ctx_ptr);
+}
+
+static void cbs_unit_uninit(CodedBitstreamContext *ctx,
+                            CodedBitstreamUnit *unit)
+{
+    if (ctx->codec->free_unit && unit->content && !unit->content_external)
+        ctx->codec->free_unit(unit);
+
+    av_freep(&unit->data);
+    unit->data_size = 0;
+    unit->data_bit_padding = 0;
+}
+
+void ff_cbs_fragment_uninit(CodedBitstreamContext *ctx,
+                            CodedBitstreamFragment *frag)
+{
+    int i;
+
+    for (i = 0; i < frag->nb_units; i++)
+        cbs_unit_uninit(ctx, &frag->units[i]);
+    av_freep(&frag->units);
+    frag->nb_units = 0;
+
+    av_freep(&frag->data);
+    frag->data_size        = 0;
+    frag->data_bit_padding = 0;
+}
+
+static int cbs_read_fragment_content(CodedBitstreamContext *ctx,
+                                     CodedBitstreamFragment *frag)
+{
+    int err, i, j;
+
+    for (i = 0; i < frag->nb_units; i++) {
+        if (ctx->decompose_unit_types) {
+            for (j = 0; j < ctx->nb_decompose_unit_types; j++) {
+                if (ctx->decompose_unit_types[j] == frag->units[i].type)
+                    break;
+            }
+            if (j >= ctx->nb_decompose_unit_types)
+                continue;
+        }
+
+        err = ctx->codec->read_unit(ctx, &frag->units[i]);
+        if (err == AVERROR(ENOSYS)) {
+            av_log(ctx->log_ctx, AV_LOG_WARNING,
+                   "Decomposition unimplemented for unit %d "
+                   "(type %"PRIu32").\n", i, frag->units[i].type);
+        } else if (err < 0) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Failed to read unit %d "
+                   "(type %"PRIu32").\n", i, frag->units[i].type);
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+int ff_cbs_read_extradata(CodedBitstreamContext *ctx,
+                          CodedBitstreamFragment *frag,
+                          const AVCodecParameters *par)
+{
+    int err;
+
+    memset(frag, 0, sizeof(*frag));
+
+    frag->data      = par->extradata;
+    frag->data_size = par->extradata_size;
+
+    err = ctx->codec->split_fragment(ctx, frag, 1);
+    if (err < 0)
+        return err;
+
+    frag->data      = NULL;
+    frag->data_size = 0;
+
+    return cbs_read_fragment_content(ctx, frag);
+}
+
+int ff_cbs_read_packet(CodedBitstreamContext *ctx,
+                       CodedBitstreamFragment *frag,
+                       const AVPacket *pkt)
+{
+    int err;
+
+    memset(frag, 0, sizeof(*frag));
+
+    frag->data      = pkt->data;
+    frag->data_size = pkt->size;
+
+    err = ctx->codec->split_fragment(ctx, frag, 0);
+    if (err < 0)
+        return err;
+
+    frag->data      = NULL;
+    frag->data_size = 0;
+
+    return cbs_read_fragment_content(ctx, frag);
+}
+
+int ff_cbs_read(CodedBitstreamContext *ctx,
+                CodedBitstreamFragment *frag,
+                const uint8_t *data, size_t size)
+{
+    int err;
+
+    memset(frag, 0, sizeof(*frag));
+
+    // (We won't write to this during split.)
+    frag->data      = (uint8_t*)data;
+    frag->data_size = size;
+
+    err = ctx->codec->split_fragment(ctx, frag, 0);
+    if (err < 0)
+        return err;
+
+    frag->data      = NULL;
+    frag->data_size = 0;
+
+    return cbs_read_fragment_content(ctx, frag);
+}
+
+
+int ff_cbs_write_fragment_data(CodedBitstreamContext *ctx,
+                               CodedBitstreamFragment *frag)
+{
+    int err, i;
+
+    for (i = 0; i < frag->nb_units; i++) {
+        if (!frag->units[i].content)
+            continue;
+
+        err = ctx->codec->write_unit(ctx, &frag->units[i]);
+        if (err < 0) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Failed to write unit %d "
+                   "(type %"PRIu32").\n", i, frag->units[i].type);
+            return err;
+        }
+    }
+
+    err = ctx->codec->assemble_fragment(ctx, frag);
+    if (err < 0) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Failed to assemble fragment.\n");
+        return err;
+    }
+
+    return 0;
+}
+
+int ff_cbs_write_extradata(CodedBitstreamContext *ctx,
+                           AVCodecParameters *par,
+                           CodedBitstreamFragment *frag)
+{
+    int err;
+
+    err = ff_cbs_write_fragment_data(ctx, frag);
+    if (err < 0)
+        return err;
+
+    av_freep(&par->extradata);
+
+    par->extradata = av_malloc(frag->data_size +
+                               AV_INPUT_BUFFER_PADDING_SIZE);
+    if (!par->extradata)
+        return AVERROR(ENOMEM);
+
+    memcpy(par->extradata, frag->data, frag->data_size);
+    memset(par->extradata + frag->data_size, 0,
+           AV_INPUT_BUFFER_PADDING_SIZE);
+    par->extradata_size = frag->data_size;
+
+    return 0;
+}
+
+int ff_cbs_write_packet(CodedBitstreamContext *ctx,
+                        AVPacket *pkt,
+                        CodedBitstreamFragment *frag)
+{
+    int err;
+
+    err = ff_cbs_write_fragment_data(ctx, frag);
+    if (err < 0)
+        return err;
+
+    err = av_new_packet(pkt, frag->data_size);
+    if (err < 0)
+        return err;
+
+    memcpy(pkt->data, frag->data, frag->data_size);
+    pkt->size = frag->data_size;
+
+    return 0;
+}
+
+
+void ff_cbs_trace_header(CodedBitstreamContext *ctx,
+                         const char *name)
+{
+    if (!ctx->trace_enable)
+        return;
+
+    av_log(ctx->log_ctx, ctx->trace_level, "%s\n", name);
+}
+
+void ff_cbs_trace_syntax_element(CodedBitstreamContext *ctx, int position,
+                                 const char *name, const char *bits,
+                                 int64_t value)
+{
+    size_t name_len, bits_len;
+    int pad;
+
+    if (!ctx->trace_enable)
+        return;
+
+    av_assert0(value >= INT_MIN && value <= UINT32_MAX);
+
+    name_len = strlen(name);
+    bits_len = strlen(bits);
+
+    if (name_len + bits_len > 60)
+        pad = bits_len + 2;
+    else
+        pad = 61 - name_len;
+
+    av_log(ctx->log_ctx, ctx->trace_level, "%-10d  %s%*s = %"PRId64"\n",
+           position, name, pad, bits, value);
+}
+
+int ff_cbs_read_unsigned(CodedBitstreamContext *ctx, GetBitContext *gbc,
+                         int width, const char *name, uint32_t *write_to,
+                         uint32_t range_min, uint32_t range_max)
+{
+    uint32_t value;
+    int position;
+
+    av_assert0(width > 0 && width <= 32);
+
+    if (get_bits_left(gbc) < width) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid value at "
+               "%s: bitstream ended.\n", name);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if (ctx->trace_enable)
+        position = get_bits_count(gbc);
+
+    value = get_bits_long(gbc, width);
+
+    if (ctx->trace_enable) {
+        char bits[33];
+        int i;
+        for (i = 0; i < width; i++)
+            bits[i] = value >> (width - i - 1) & 1 ? '1' : '0';
+        bits[i] = 0;
+
+        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;
+}
+
+int ff_cbs_write_unsigned(CodedBitstreamContext *ctx, PutBitContext *pbc,
+                          int width, const char *name, uint32_t value,
+                          uint32_t range_min, uint32_t range_max)
+{
+    av_assert0(width > 0 && width <= 32);
+
+    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;
+    }
+
+    if (put_bits_left(pbc) < width)
+        return AVERROR(ENOSPC);
+
+    if (ctx->trace_enable) {
+        char bits[33];
+        int i;
+        for (i = 0; i < width; i++)
+            bits[i] = value >> (width - i - 1) & 1 ? '1' : '0';
+        bits[i] = 0;
+
+        ff_cbs_trace_syntax_element(ctx, put_bits_count(pbc), name, bits, value);
+    }
+
+    if (width < 32)
+        put_bits(pbc, width, value);
+    else
+        put_bits32(pbc, value);
+
+    return 0;
+}
+
+
+static int cbs_insert_unit(CodedBitstreamContext *ctx,
+                           CodedBitstreamFragment *frag,
+                           int position)
+{
+    CodedBitstreamUnit *units;
+
+    units = av_malloc_array(frag->nb_units + 1, sizeof(*units));
+    if (!units)
+        return AVERROR(ENOMEM);
+
+    if (position > 0)
+        memcpy(units, frag->units, position * sizeof(*units));
+    if (position < frag->nb_units)
+        memcpy(units + position + 1, frag->units + position,
+               (frag->nb_units - position) * sizeof(*units));
+
+    memset(units + position, 0, sizeof(*units));
+
+    av_freep(&frag->units);
+    frag->units = units;
+    ++frag->nb_units;
+
+    return 0;
+}
+
+int ff_cbs_insert_unit_content(CodedBitstreamContext *ctx,
+                               CodedBitstreamFragment *frag,
+                               int position,
+                               CodedBitstreamUnitType type,
+                               void *content)
+{
+    int err;
+
+    if (position == -1)
+        position = frag->nb_units;
+    av_assert0(position >= 0 && position <= frag->nb_units);
+
+    err = cbs_insert_unit(ctx, frag, position);
+    if (err < 0)
+        return err;
+
+    frag->units[position].type             = type;
+    frag->units[position].content          = content;
+    frag->units[position].content_external = 1;
+
+    return 0;
+}
+
+int ff_cbs_insert_unit_data(CodedBitstreamContext *ctx,
+                            CodedBitstreamFragment *frag,
+                            int position,
+                            CodedBitstreamUnitType type,
+                            uint8_t *data, size_t data_size)
+{
+    int err;
+
+    if (position == -1)
+        position = frag->nb_units;
+    av_assert0(position >= 0 && position <= frag->nb_units);
+
+    err = cbs_insert_unit(ctx, frag, position);
+    if (err < 0)
+        return err;
+
+    frag->units[position].type      = type;
+    frag->units[position].data      = data;
+    frag->units[position].data_size = data_size;
+
+    return 0;
+}
+
+int ff_cbs_delete_unit(CodedBitstreamContext *ctx,
+                       CodedBitstreamFragment *frag,
+                       int position)
+{
+    if (position < 0 || position >= frag->nb_units)
+        return AVERROR(EINVAL);
+
+    cbs_unit_uninit(ctx, &frag->units[position]);
+
+    --frag->nb_units;
+
+    if (frag->nb_units == 0) {
+        av_freep(&frag->units);
+
+    } else {
+        memmove(frag->units + position,
+                frag->units + position + 1,
+                (frag->nb_units - position) * sizeof(*frag->units));
+
+        // Don't bother reallocating the unit array.
+    }
+
+    return 0;
+}
diff --git a/libavcodec/cbs.h b/libavcodec/cbs.h
new file mode 100644
index 0000000000..2dc975ed79
--- /dev/null
+++ b/libavcodec/cbs.h
@@ -0,0 +1,308 @@
+/*
+ * 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
+ */
+
+#ifndef AVCODEC_CBS_H
+#define AVCODEC_CBS_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "avcodec.h"
+
+
+/*
+ * This defines a framework for converting between a coded bitstream
+ * and structures defining all individual syntax elements found in
+ * such a stream.
+ *
+ * Conversion in both directions is possible.  Given a coded bitstream
+ * (any meaningful fragment), it can be parsed and decomposed into
+ * syntax elements stored in a set of codec-specific structures.
+ * Similarly, given a set of those same codec-specific structures the
+ * syntax elements can be serialised and combined to create a coded
+ * bitstream.
+ */
+
+struct CodedBitstreamType;
+
+/**
+ * The codec-specific type of a bitstream unit.
+ */
+typedef uint32_t CodedBitstreamUnitType;
+
+/**
+ * Coded bitstream unit structure.
+ *
+ * A bitstream unit the smallest element of a bitstream which
+ * is meaningful on its own.  For example, an H.264 NAL unit.
+ *
+ * See the codec-specific header for the meaning of this for any
+ * particular codec.
+ */
+typedef struct CodedBitstreamUnit {
+    /**
+     * Codec-specific type of this unit.
+     */
+    CodedBitstreamUnitType type;
+
+    /**
+     * Pointer to the directly-parsable bitstream form of this unit.
+     *
+     * May be NULL if the unit currently only exists in decomposed form.
+     */
+    uint8_t *data;
+    /**
+     * The number of bytes in the bitstream (including any padding bits
+     * in the final byte).
+     */
+    size_t   data_size;
+    /**
+     * The number of bits which should be ignored in the final byte.
+     *
+     * This supports non-byte-aligned bitstreams.
+     */
+    size_t   data_bit_padding;
+
+    /**
+     * Pointer to the decomposed form of this unit.
+     *
+     * The type of this structure depends on both the codec and the
+     * type of this unit.  May be NULL if the unit only exists in
+     * bitstream form.
+     */
+    void *content;
+    /**
+     * Whether the content was supplied externally.
+     *
+     * If so, it should not be freed when freeing the unit.
+     */
+    int   content_external;
+} CodedBitstreamUnit;
+
+/**
+ * Coded bitstream fragment structure, combining one or more units.
+ *
+ * This is any sequence of units.  It need not form some greater whole,
+ * though in many cases it will.  For example, an H.264 access unit,
+ * which is composed of a sequence of H.264 NAL units.
+ */
+typedef struct CodedBitstreamFragment {
+    /**
+     * Pointer to the bitstream form of this fragment.
+     *
+     * May be NULL if the fragment only exists as component units.
+     */
+    uint8_t *data;
+    /**
+     * The number of bytes in the bitstream.
+     *
+     * The number of bytes in the bitstream (including any padding bits
+     * in the final byte).
+     */
+    size_t   data_size;
+    /**
+     * The number of bits which should be ignored in the final byte.
+     */
+    size_t data_bit_padding;
+
+    /**
+     * Number of units in this fragment.
+     *
+     * This may be zero if the fragment only exists in bitstream form
+     * and has not been decomposed.
+     */
+    int              nb_units;
+    /**
+     * Pointer to an array of units of length nb_units.
+     *
+     * Must be NULL if nb_units is zero.
+     */
+    CodedBitstreamUnit *units;
+} CodedBitstreamFragment;
+
+/**
+ * Context structure for coded bitstream operations.
+ */
+typedef struct CodedBitstreamContext {
+    /**
+     * Logging context to be passed to all av_log() calls associated
+     * with this context.
+     */
+    void *log_ctx;
+
+    /**
+     * Internal codec-specific hooks.
+     */
+    const struct CodedBitstreamType *codec;
+
+    /**
+     * Internal codec-specific data.
+     *
+     * This contains any information needed when reading/writing
+     * bitsteams which will not necessarily be present in a fragment.
+     * For example, for H.264 it contains all currently visible
+     * parameter sets - they are required to determine the bitstream
+     * syntax but need not be present in every access unit.
+     */
+    void *priv_data;
+
+    /**
+     * Array of unit types which should be decomposed when reading.
+     *
+     * Types not in this list will be available in bitstream form only.
+     * If NULL, all supported types will be decomposed.
+     */
+    CodedBitstreamUnitType *decompose_unit_types;
+    /**
+     * Length of the decompose_unit_types array.
+     */
+    int nb_decompose_unit_types;
+
+    /**
+     * Enable trace output during read/write operations.
+     */
+    int trace_enable;
+    /**
+     * Log level to use for trace output.
+     *
+     * From AV_LOG_*; defaults to AV_LOG_TRACE.
+     */
+    int trace_level;
+} CodedBitstreamContext;
+
+
+/**
+ * Create and initialise a new context for the given codec.
+ */
+int ff_cbs_init(CodedBitstreamContext **ctx,
+                enum AVCodecID codec_id, void *log_ctx);
+
+/**
+ * Close a context and free all internal state.
+ */
+void ff_cbs_close(CodedBitstreamContext **ctx);
+
+
+/**
+ * Read the extradata bitstream found in codec parameters into a
+ * fragment, then split into units and decompose.
+ *
+ * This also updates the internal state, so will need to be called for
+ * codecs with extradata to read parameter sets necessary for further
+ * parsing even if the fragment itself is not desired.
+ */
+int ff_cbs_read_extradata(CodedBitstreamContext *ctx,
+                          CodedBitstreamFragment *frag,
+                          const AVCodecParameters *par);
+
+/**
+ * Read the data bitstream from a packet into a fragment, then
+ * split into units and decompose.
+ *
+ * This also updates the internal state of the coded bitstream context
+ * with any persistent data from the fragment which may be required to
+ * read following fragments (e.g. parameter sets).
+ */
+int ff_cbs_read_packet(CodedBitstreamContext *ctx,
+                       CodedBitstreamFragment *frag,
+                       const AVPacket *pkt);
+
+/**
+ * Read a bitstream from a memory region into a fragment, then
+ * split into units and decompose.
+ *
+ * This also updates the internal state of the coded bitstream context
+ * with any persistent data from the fragment which may be required to
+ * read following fragments (e.g. parameter sets).
+ */
+int ff_cbs_read(CodedBitstreamContext *ctx,
+                CodedBitstreamFragment *frag,
+                const uint8_t *data, size_t size);
+
+
+/**
+ * Write the content of the fragment to its own internal buffer.
+ *
+ * Writes the content of all units and then assembles them into a new
+ * data buffer.  When modifying the content of decomposed units, this
+ * can be used to regenerate the bitstream form of units or the whole
+ * fragment so that it can be extracted for other use.
+ *
+ * This also updates the internal state of the coded bitstream context
+ * with any persistent data from the fragment which may be required to
+ * write following fragments (e.g. parameter sets).
+ */
+int ff_cbs_write_fragment_data(CodedBitstreamContext *ctx,
+                               CodedBitstreamFragment *frag);
+
+/**
+ * Write the bitstream of a fragment to the extradata in codec parameters.
+ *
+ * This replaces any existing extradata in the structure.
+ */
+int ff_cbs_write_extradata(CodedBitstreamContext *ctx,
+                           AVCodecParameters *par,
+                           CodedBitstreamFragment *frag);
+
+/**
+ * Write the bitstream of a fragment to a packet.
+ */
+int ff_cbs_write_packet(CodedBitstreamContext *ctx,
+                        AVPacket *pkt,
+                        CodedBitstreamFragment *frag);
+
+
+/**
+ * Free all allocated memory in a fragment.
+ */
+void ff_cbs_fragment_uninit(CodedBitstreamContext *ctx,
+                            CodedBitstreamFragment *frag);
+
+
+/**
+ * Insert a new unit into a fragment with the given content.
+ *
+ * The content structure continues to be owned by the caller, and
+ * will not be freed when the unit is.
+ */
+int ff_cbs_insert_unit_content(CodedBitstreamContext *ctx,
+                               CodedBitstreamFragment *frag,
+                               int position,
+                               CodedBitstreamUnitType type,
+                               void *content);
+
+/**
+ * Insert a new unit into a fragment with the given data bitstream.
+ *
+ * The data buffer will be owned by the unit after this operation.
+ */
+int ff_cbs_insert_unit_data(CodedBitstreamContext *ctx,
+                            CodedBitstreamFragment *frag,
+                            int position,
+                            CodedBitstreamUnitType type,
+                            uint8_t *data, size_t data_size);
+
+/**
+ * Delete a unit from a fragment and free all memory it uses.
+ */
+int ff_cbs_delete_unit(CodedBitstreamContext *ctx,
+                       CodedBitstreamFragment *frag,
+                       int position);
+
+
+#endif /* AVCODEC_CBS_H */
diff --git a/libavcodec/cbs_internal.h b/libavcodec/cbs_internal.h
new file mode 100644
index 0000000000..f6a42beea3
--- /dev/null
+++ b/libavcodec/cbs_internal.h
@@ -0,0 +1,86 @@
+/*
+ * 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
+ */
+
+#ifndef AVCODEC_CBS_INTERNAL_H
+#define AVCODEC_CBS_INTERNAL_H
+
+#include "avcodec.h"
+#include "cbs.h"
+#include "get_bits.h"
+#include "put_bits.h"
+
+
+typedef struct CodedBitstreamType {
+    enum AVCodecID codec_id;
+
+    size_t priv_data_size;
+
+    // Split frag->data into coded bitstream units, creating the
+    // frag->units array.  Fill data but not content on each unit.
+    // header is set if the fragment came from a header block, which
+    // may require different parsing for some codecs (e.g. the AVCC
+    // header in H.264).
+    int (*split_fragment)(CodedBitstreamContext *ctx,
+                          CodedBitstreamFragment *frag,
+                          int header);
+
+    // Read the unit->data bitstream and decompose it, creating
+    // unit->content.
+    int (*read_unit)(CodedBitstreamContext *ctx,
+                     CodedBitstreamUnit *unit);
+
+    // Write the unit->data bitstream from unit->content.
+    int (*write_unit)(CodedBitstreamContext *ctx,
+                      CodedBitstreamUnit *unit);
+
+    // Read the data from all of frag->units and assemble it into
+    // a bitstream for the whole fragment.
+    int (*assemble_fragment)(CodedBitstreamContext *ctx,
+                             CodedBitstreamFragment *frag);
+
+    // Free the content and data of a single unit.
+    void (*free_unit)(CodedBitstreamUnit *unit);
+
+    // Free the codec internal state.
+    void (*close)(CodedBitstreamContext *ctx);
+} CodedBitstreamType;
+
+
+// Helper functions for trace output.
+
+void ff_cbs_trace_header(CodedBitstreamContext *ctx,
+                         const char *name);
+
+void ff_cbs_trace_syntax_element(CodedBitstreamContext *ctx,
+                                 int position, const char *name,
+                                 const char *bitstring, int64_t value);
+
+
+// Helper functions for read/write of common bitstream elements, including
+// generation of trace output.
+
+int ff_cbs_read_unsigned(CodedBitstreamContext *ctx, GetBitContext *gbc,
+                         int width, const char *name, uint32_t *write_to,
+                         uint32_t range_min, uint32_t range_max);
+
+int ff_cbs_write_unsigned(CodedBitstreamContext *ctx, PutBitContext *pbc,
+                          int width, const char *name, uint32_t value,
+                          uint32_t range_min, uint32_t range_max);
+
+
+#endif /* AVCODEC_CBS_INTERNAL_H */