[FFmpeg-devel] [PATCH 1/5] avformat: introduce AVStreamGroup

James Almer jamrial at gmail.com
Tue Nov 21 23:14:38 EET 2023


Signed-off-by: James Almer <jamrial at gmail.com>
---
 libavformat/avformat.c | 178 +++++++++++++++++++++++++++++++++++++++--
 libavformat/avformat.h | 163 +++++++++++++++++++++++++++++++++++++
 libavformat/dump.c     |  33 ++++++--
 libavformat/internal.h |  33 ++++++++
 libavformat/options.c  |  90 +++++++++++++++++++++
 5 files changed, 486 insertions(+), 11 deletions(-)

diff --git a/libavformat/avformat.c b/libavformat/avformat.c
index 5b8bb7879e..4e31924c71 100644
--- a/libavformat/avformat.c
+++ b/libavformat/avformat.c
@@ -80,6 +80,25 @@ FF_ENABLE_DEPRECATION_WARNINGS
     av_freep(pst);
 }
 
+void ff_free_stream_group(AVStreamGroup **pstg)
+{
+    AVStreamGroup *stg = *pstg;
+
+    if (!stg)
+        return;
+
+    av_freep(&stg->streams);
+    av_dict_free(&stg->metadata);
+    av_freep(&stg->priv_data);
+    switch (stg->type) {
+    // Structs in the union are freed here
+    default:
+        break;
+    }
+
+    av_freep(pstg);
+}
+
 void ff_remove_stream(AVFormatContext *s, AVStream *st)
 {
     av_assert0(s->nb_streams>0);
@@ -88,6 +107,14 @@ void ff_remove_stream(AVFormatContext *s, AVStream *st)
     ff_free_stream(&s->streams[ --s->nb_streams ]);
 }
 
+void ff_remove_stream_group(AVFormatContext *s, AVStreamGroup *stg)
+{
+    av_assert0(s->nb_stream_groups > 0);
+    av_assert0(s->stream_groups[ s->nb_stream_groups - 1 ] == stg);
+
+    ff_free_stream_group(&s->stream_groups[ --s->nb_stream_groups ]);
+}
+
 /* XXX: suppress the packet queue */
 void ff_flush_packet_queue(AVFormatContext *s)
 {
@@ -118,6 +145,9 @@ void avformat_free_context(AVFormatContext *s)
 
     for (unsigned i = 0; i < s->nb_streams; i++)
         ff_free_stream(&s->streams[i]);
+    for (unsigned i = 0; i < s->nb_stream_groups; i++)
+        ff_free_stream_group(&s->stream_groups[i]);
+    s->nb_stream_groups = 0;
     s->nb_streams = 0;
 
     for (unsigned i = 0; i < s->nb_programs; i++) {
@@ -138,6 +168,7 @@ void avformat_free_context(AVFormatContext *s)
     av_dict_free(&si->id3v2_meta);
     av_packet_free(&si->pkt);
     av_packet_free(&si->parse_pkt);
+    av_freep(&s->stream_groups);
     av_freep(&s->streams);
     ff_flush_packet_queue(s);
     av_freep(&s->url);
@@ -464,7 +495,7 @@ int av_find_best_stream(AVFormatContext *ic, enum AVMediaType type,
  */
 static int match_stream_specifier(const AVFormatContext *s, const AVStream *st,
                                   const char *spec, const char **indexptr,
-                                  const AVProgram **p)
+                                  const AVStreamGroup **g, const AVProgram **p)
 {
     int match = 1;                      /* Stores if the specifier matches so far. */
     while (*spec) {
@@ -493,6 +524,46 @@ static int match_stream_specifier(const AVFormatContext *s, const AVStream *st,
                 match = 0;
             if (nopic && (st->disposition & AV_DISPOSITION_ATTACHED_PIC))
                 match = 0;
+        } else if (*spec == 'g' && *(spec + 1) == ':') {
+            int64_t group_idx = -1, group_id = -1;
+            int found = 0;
+            char *endptr;
+            spec += 2;
+            if (*spec == '#' || (*spec == 'i' && *(spec + 1) == ':')) {
+                spec += 1 + (*spec == 'i');
+                group_id = strtol(spec, &endptr, 0);
+                if (spec == endptr || (*endptr && *endptr++ != ':'))
+                    return AVERROR(EINVAL);
+                spec = endptr;
+            } else {
+                group_idx = strtol(spec, &endptr, 0);
+                /* Disallow empty id and make sure that if we are not at the end, then another specifier must follow. */
+                if (spec == endptr || (*endptr && *endptr++ != ':'))
+                    return AVERROR(EINVAL);
+                spec = endptr;
+            }
+            if (match) {
+                if (group_id > 0) {
+                    for (unsigned i = 0; i < s->nb_stream_groups; i++) {
+                        if (group_id == s->stream_groups[i]->id) {
+                            group_idx = i;
+                            break;
+                        }
+                    }
+			    }
+                if (group_idx < 0 || group_idx > s->nb_stream_groups)
+                    return AVERROR(EINVAL);
+                for (unsigned j = 0; j < s->stream_groups[group_idx]->nb_streams; j++) {
+                    if (st->index == s->stream_groups[group_idx]->streams[j]->index) {
+                        found = 1;
+                        if (g)
+                            *g = s->stream_groups[group_idx];
+                        break;
+                    }
+                }
+            }
+            if (!found)
+                match = 0;
         } else if (*spec == 'p' && *(spec + 1) == ':') {
             int prog_id;
             int found = 0;
@@ -592,9 +663,10 @@ int avformat_match_stream_specifier(AVFormatContext *s, AVStream *st,
     char *endptr;
     const char *indexptr = NULL;
     const AVProgram *p = NULL;
+    const AVStreamGroup *g = NULL;
     int nb_streams;
 
-    ret = match_stream_specifier(s, st, spec, &indexptr, &p);
+    ret = match_stream_specifier(s, st, spec, &indexptr, &g, &p);
     if (ret < 0)
         goto error;
 
@@ -612,10 +684,11 @@ int avformat_match_stream_specifier(AVFormatContext *s, AVStream *st,
         return (index == st->index);
 
     /* If we requested a matching stream index, we have to ensure st is that. */
-    nb_streams = p ? p->nb_stream_indexes : s->nb_streams;
+    nb_streams = g ? g->nb_streams : (p ? p->nb_stream_indexes : s->nb_streams);
     for (int i = 0; i < nb_streams && index >= 0; i++) {
-        const AVStream *candidate = s->streams[p ? p->stream_index[i] : i];
-        ret = match_stream_specifier(s, candidate, spec, NULL, NULL);
+        unsigned idx = g ? g->streams[i]->index : (p ? p->stream_index[i] : i);
+        const AVStream *candidate = s->streams[idx];
+        ret = match_stream_specifier(s, candidate, spec, NULL, NULL, NULL);
         if (ret < 0)
             goto error;
         if (ret > 0 && index-- == 0 && st == candidate)
@@ -629,6 +702,101 @@ error:
     return ret;
 }
 
+
+/**
+ * Matches a stream specifier (but ignores requested index).
+ *
+ * @param indexptr set to point to the requested stream index if there is one
+ *
+ * @return <0 on error
+ *         0  if st is NOT a matching stream
+ *         >0 if st is a matching stream
+ */
+static int match_stream_group_specifier(const AVFormatContext *s, const AVStreamGroup *stg,
+                                        const char *spec, const char **indexptr)
+{
+    int match = 1;                      /* Stores if the specifier matches so far. */
+    while (*spec) {
+        if (*spec <= '9' && *spec >= '0') { /* opt:index */
+            if (indexptr)
+                *indexptr = spec;
+            return match;
+        } else if (*spec == 't' && *(spec + 1) == ':') {
+            int64_t group_type = -1;
+            int found = 0;
+            char *endptr;
+            spec += 2;
+            group_type = strtol(spec, &endptr, 0);
+            /* Disallow empty type and make sure that if we are not at the end, then another specifier must follow. */
+            if (spec == endptr || (*endptr && *endptr++ != ':'))
+                return AVERROR(EINVAL);
+            spec = endptr;
+            if (match && group_type > 0) {
+                for (unsigned i = 0; i < s->nb_stream_groups; i++) {
+                    if (group_type == s->stream_groups[i]->type) {
+                        found = 1;
+                        break;
+                    }
+			    }
+            }
+            if (!found)
+                match = 0;
+        } else if (*spec == '#' ||
+                   (*spec == 'i' && *(spec + 1) == ':')) {
+            int group_id;
+            char *endptr;
+            spec += 1 + (*spec == 'i');
+            group_id = strtol(spec, &endptr, 0);
+            if (spec == endptr || *endptr)                /* Disallow empty id and make sure we are at the end. */
+                return AVERROR(EINVAL);
+            return match && (group_id == stg->id);
+        }
+    }
+
+    return match;
+}
+
+int avformat_match_stream_group_specifier(AVFormatContext *s, AVStreamGroup *stg,
+                                          const char *spec)
+{
+    int ret, index;
+    char *endptr;
+    const char *indexptr = NULL;
+
+    ret = match_stream_group_specifier(s, stg, spec, &indexptr);
+    if (ret < 0)
+        goto error;
+
+    if (!indexptr)
+        return ret;
+
+    index = strtol(indexptr, &endptr, 0);
+    if (*endptr) {                  /* We can't have anything after the requested index. */
+        ret = AVERROR(EINVAL);
+        goto error;
+    }
+
+    /* This is not really needed but saves us a loop for simple stream index specifiers. */
+    if (spec == indexptr)
+        return (index == stg->index);
+
+    /* If we requested a matching stream index, we have to ensure stg is that. */
+    for (int i = 0; i < s->nb_stream_groups && index >= 0; i++) {
+        const AVStreamGroup *candidate = s->stream_groups[i];
+        ret = match_stream_group_specifier(s, candidate, spec, NULL);
+        if (ret < 0)
+            goto error;
+        if (ret > 0 && index-- == 0 && stg == candidate)
+            return 1;
+    }
+    return 0;
+
+error:
+    if (ret == AVERROR(EINVAL))
+        av_log(s, AV_LOG_ERROR, "Invalid stream group specifier: %s.\n", spec);
+    return ret;
+}
+
 AVRational av_guess_sample_aspect_ratio(AVFormatContext *format, AVStream *stream, AVFrame *frame)
 {
     AVRational undef = {0, 1};
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 9e7eca007e..0b4ae096d5 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -1018,6 +1018,77 @@ typedef struct AVStream {
     int pts_wrap_bits;
 } AVStream;
 
+enum AVStreamGroupParamsType {
+    AV_STREAM_GROUP_PARAMS_NONE,
+};
+
+typedef struct AVStreamGroup {
+    /**
+     * A class for @ref avoptions. Set by avformat_stream_group_create().
+     */
+    const AVClass *av_class;
+
+    void *priv_data;
+
+    /**
+     * Group index in AVFormatContext.
+     */
+    unsigned int index;
+
+    /**
+     * Group type-specific group ID.
+     *
+     * decoding: set by libavformat
+     * encoding: may set by the user, replaced by libavformat if left unset
+     */
+    int64_t id;
+
+    /**
+     * Group type
+     *
+     * decoding: set by libavformat on group creation
+     * encoding: set by avformat_stream_group_create()
+     */
+    enum AVStreamGroupParamsType type;
+
+    /**
+     * Group type-specific parameters
+     */
+    union {
+        uintptr_t dummy; // Placeholder
+    } params;
+
+    /**
+     * Metadata that applies to the whole group.
+     *
+     * - demuxing: set by libavformat on group creation
+     * - muxing: may be set by the caller before avformat_write_header()
+     *
+     * Freed by libavformat in avformat_free_context().
+     */
+    AVDictionary *metadata;
+
+    /**
+     * Number of elements in AVStreamGroup.streams.
+     *
+     * Set by avformat_stream_group_add_stream() must not be modified by any other code.
+     */
+    unsigned int nb_streams;
+
+    /**
+     * A list of streams in the group. New entries are created with
+     * avformat_stream_group_add_stream().
+     *
+     * - demuxing: entries are created by libavformat on group creation.
+     *             If AVFMTCTX_NOHEADER is set in ctx_flags, then new entries may also
+     *             appear in av_read_frame().
+     * - muxing: entries are created by the user before avformat_write_header().
+     *
+     * Freed by libavformat in avformat_free_context().
+     */
+    AVStream **streams;
+} AVStreamGroup;
+
 struct AVCodecParserContext *av_stream_get_parser(const AVStream *s);
 
 #if FF_API_GET_END_PTS
@@ -1726,6 +1797,26 @@ typedef struct AVFormatContext {
      * @return 0 on success, a negative AVERROR code on failure
      */
     int (*io_close2)(struct AVFormatContext *s, AVIOContext *pb);
+
+    /**
+     * Number of elements in AVFormatContext.stream_groups.
+     *
+     * Set by avformat_stream_group_create(), must not be modified by any other code.
+     */
+    unsigned int nb_stream_groups;
+
+    /**
+     * A list of all stream groups in the file. New groups are created with
+     * avformat_stream_group_create(), and filled with avformat_stream_group_add_stream().
+     *
+     * - demuxing: groups may be created by libavformat in avformat_open_input().
+     *             If AVFMTCTX_NOHEADER is set in ctx_flags, then new groups may also
+     *             appear in av_read_frame().
+     * - muxing: groups may be created by the user before avformat_write_header().
+     *
+     * Freed by libavformat in avformat_free_context().
+     */
+    AVStreamGroup **stream_groups;
 } AVFormatContext;
 
 /**
@@ -1844,6 +1935,37 @@ const AVClass *avformat_get_class(void);
  */
 const AVClass *av_stream_get_class(void);
 
+/**
+ * Get the AVClass for AVStreamGroup. It can be used in combination with
+ * AV_OPT_SEARCH_FAKE_OBJ for examining options.
+ *
+ * @see av_opt_find().
+ */
+const AVClass *av_stream_group_get_class(void);
+
+/**
+ * Add a new empty stream group to a media file.
+ *
+ * When demuxing, it may be called by the demuxer in read_header(). If the
+ * flag AVFMTCTX_NOHEADER is set in s.ctx_flags, then it may also
+ * be called in read_packet().
+ *
+ * When muxing, may be called by the user before avformat_write_header().
+ *
+ * User is required to call avformat_free_context() to clean up the allocation
+ * by avformat_stream_group_create().
+ *
+ * New streams can be added to the group with avformat_stream_group_add_stream().
+ *
+ * @param s media file handle
+ *
+ * @return newly created group or NULL on error.
+ * @see avformat_new_stream, avformat_stream_group_add_stream.
+ */
+AVStreamGroup *avformat_stream_group_create(AVFormatContext *s,
+                                            enum AVStreamGroupParamsType type,
+                                            AVDictionary **options);
+
 /**
  * Add a new stream to a media file.
  *
@@ -1863,6 +1985,31 @@ const AVClass *av_stream_get_class(void);
  */
 AVStream *avformat_new_stream(AVFormatContext *s, const struct AVCodec *c);
 
+/**
+ * Add an already allocated stream to a stream group.
+ *
+ * When demuxing, it may be called by the demuxer in read_header(). If the
+ * flag AVFMTCTX_NOHEADER is set in s.ctx_flags, then it may also
+ * be called in read_packet().
+ *
+ * When muxing, may be called by the user before avformat_write_header() after
+ * having allocated a new group with avformat_stream_group_create() and stream with
+ * avformat_new_stream().
+ *
+ * User is required to call avformat_free_context() to clean up the allocation
+ * by avformat_stream_group_add_stream().
+ *
+ * @param stg stream group belonging to a media file.
+ * @param st  stream in the media file to add to the group.
+ *
+ * @retval 0                 success
+ * @retval AVERROR(EEXIST)   the stream was already in the group
+ * @retval "another negative error code" legitimate errors
+ *
+ * @see avformat_new_stream, avformat_stream_group_create.
+ */
+int avformat_stream_group_add_stream(AVStreamGroup *stg, AVStream *st);
+
 #if FF_API_AVSTREAM_SIDE_DATA
 /**
  * Wrap an existing array as stream side data.
@@ -2819,6 +2966,22 @@ AVRational av_guess_frame_rate(AVFormatContext *ctx, AVStream *stream,
 int avformat_match_stream_specifier(AVFormatContext *s, AVStream *st,
                                     const char *spec);
 
+/**
+ * Check if the group stg contained in s is matched by the stream group
+ * specifier spec.
+ *
+ * See the "stream group specifiers" chapter in the documentation for the
+ * syntax of spec.
+ *
+ * @return  >0 if stg is matched by spec;
+ *          0  if stg is not matched by spec;
+ *          AVERROR code if spec is invalid
+ *
+ * @note  A stream group specifier can match several groups in the format.
+ */
+int avformat_match_stream_group_specifier(AVFormatContext *s, AVStreamGroup *stg,
+                                          const char *spec);
+
 int avformat_queue_attached_pictures(AVFormatContext *s);
 
 enum AVTimebaseSource {
diff --git a/libavformat/dump.c b/libavformat/dump.c
index c0868a1bb3..ededeedaa9 100644
--- a/libavformat/dump.c
+++ b/libavformat/dump.c
@@ -509,7 +509,7 @@ static void dump_sidedata(void *ctx, const AVStream *st, const char *indent)
 
 /* "user interface" functions */
 static void dump_stream_format(const AVFormatContext *ic, int i,
-                               int index, int is_output)
+                               int group_index, int index, int is_output)
 {
     char buf[256];
     int flags = (is_output ? ic->oformat->flags : ic->iformat->flags);
@@ -517,6 +517,8 @@ static void dump_stream_format(const AVFormatContext *ic, int i,
     const FFStream *const sti = cffstream(st);
     const AVDictionaryEntry *lang = av_dict_get(st->metadata, "language", NULL, 0);
     const char *separator = ic->dump_separator;
+    const char *group_indent = group_index >= 0 ? "    " : "";
+    const char *extra_indent = group_index >= 0 ? "        " : "      ";
     AVCodecContext *avctx;
     int ret;
 
@@ -543,7 +545,8 @@ static void dump_stream_format(const AVFormatContext *ic, int i,
     avcodec_string(buf, sizeof(buf), avctx, is_output);
     avcodec_free_context(&avctx);
 
-    av_log(NULL, AV_LOG_INFO, "  Stream #%d:%d", index, i);
+    av_log(NULL, AV_LOG_INFO, "%s  Stream #%d", group_indent, index);
+    av_log(NULL, AV_LOG_INFO, ":%d", i);
 
     /* the pid is an important information, so we display it */
     /* XXX: add a generic system */
@@ -621,9 +624,24 @@ static void dump_stream_format(const AVFormatContext *ic, int i,
         av_log(NULL, AV_LOG_INFO, " (non-diegetic)");
     av_log(NULL, AV_LOG_INFO, "\n");
 
-    dump_metadata(NULL, st->metadata, "    ");
+    dump_metadata(NULL, st->metadata, extra_indent);
 
-    dump_sidedata(NULL, st, "    ");
+    dump_sidedata(NULL, st, extra_indent);
+}
+
+static void dump_stream_group(const AVFormatContext *ic, uint8_t *printed,
+                              int i, int index, int is_output)
+{
+    const AVStreamGroup *stg = ic->stream_groups[i];
+    char buf[512];
+    int ret;
+
+    av_log(NULL, AV_LOG_INFO, "  Stream group #%d:%d[0x%"PRIx64"]:", index, i, stg->id);
+
+    switch (stg->type) {
+    default:
+        break;
+    }
 }
 
 void av_dump_format(AVFormatContext *ic, int index,
@@ -699,7 +717,7 @@ void av_dump_format(AVFormatContext *ic, int index,
             dump_metadata(NULL, program->metadata, "    ");
             for (k = 0; k < program->nb_stream_indexes; k++) {
                 dump_stream_format(ic, program->stream_index[k],
-                                   index, is_output);
+                                   -1, index, is_output);
                 printed[program->stream_index[k]] = 1;
             }
             total += program->nb_stream_indexes;
@@ -708,9 +726,12 @@ void av_dump_format(AVFormatContext *ic, int index,
             av_log(NULL, AV_LOG_INFO, "  No Program\n");
     }
 
+    for (i = 0; i < ic->nb_stream_groups; i++)
+         dump_stream_group(ic, printed, i, index, is_output);
+
     for (i = 0; i < ic->nb_streams; i++)
         if (!printed[i])
-            dump_stream_format(ic, i, index, is_output);
+            dump_stream_format(ic, i, -1, index, is_output);
 
     av_free(printed);
 }
diff --git a/libavformat/internal.h b/libavformat/internal.h
index 7702986c9c..c6181683ef 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -202,6 +202,7 @@ typedef struct FFStream {
      */
     AVStream pub;
 
+    AVFormatContext *fmtctx;
     /**
      * Set to 1 if the codec allows reordering, so pts can be different
      * from dts.
@@ -427,6 +428,26 @@ static av_always_inline const FFStream *cffstream(const AVStream *st)
     return (const FFStream*)st;
 }
 
+typedef struct FFStreamGroup {
+    /**
+     * The public context.
+     */
+    AVStreamGroup pub;
+
+    AVFormatContext *fmtctx;
+} FFStreamGroup;
+
+
+static av_always_inline FFStreamGroup *ffstreamgroup(AVStreamGroup *stg)
+{
+    return (FFStreamGroup*)stg;
+}
+
+static av_always_inline const FFStreamGroup *cffstreamgroup(const AVStreamGroup *stg)
+{
+    return (const FFStreamGroup*)stg;
+}
+
 #ifdef __GNUC__
 #define dynarray_add(tab, nb_ptr, elem)\
 do {\
@@ -608,6 +629,18 @@ void ff_free_stream(AVStream **st);
  */
 void ff_remove_stream(AVFormatContext *s, AVStream *st);
 
+/**
+ * Frees a stream group without modifying the corresponding AVFormatContext.
+ * Must only be called if the latter doesn't matter or if the stream
+ * is not yet attached to an AVFormatContext.
+ */
+void ff_free_stream_group(AVStreamGroup **pstg);
+/**
+ * Remove a stream group from its AVFormatContext and free it.
+ * The group must be the last stream of the AVFormatContext.
+ */
+void ff_remove_stream_group(AVFormatContext *s, AVStreamGroup *stg);
+
 unsigned int ff_codec_get_tag(const AVCodecTag *tags, enum AVCodecID id);
 
 enum AVCodecID ff_codec_get_id(const AVCodecTag *tags, unsigned int tag);
diff --git a/libavformat/options.c b/libavformat/options.c
index 1d8c52246b..9ddc28842c 100644
--- a/libavformat/options.c
+++ b/libavformat/options.c
@@ -271,6 +271,7 @@ AVStream *avformat_new_stream(AVFormatContext *s, const AVCodec *c)
     if (!st->codecpar)
         goto fail;
 
+    sti->fmtctx = s;
     sti->avctx = avcodec_alloc_context3(NULL);
     if (!sti->avctx)
         goto fail;
@@ -325,6 +326,95 @@ fail:
     return NULL;
 }
 
+static const AVOption stream_group_options[] = {
+    {"id", "Set group id", offsetof(AVStreamGroup, id), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX, AV_OPT_FLAG_ENCODING_PARAM },
+    { NULL }
+};
+
+static const AVClass stream_group_class = {
+    .class_name     = "AVStreamGroup",
+    .item_name      = av_default_item_name,
+    .version        = LIBAVUTIL_VERSION_INT,
+    .option         = stream_group_options,
+};
+
+const AVClass *av_stream_group_get_class(void)
+{
+    return &stream_group_class;
+}
+
+AVStreamGroup *avformat_stream_group_create(AVFormatContext *s,
+                                            enum AVStreamGroupParamsType type,
+                                            AVDictionary **options)
+{
+    AVStreamGroup **stream_groups;
+    AVStreamGroup *stg;
+    FFStreamGroup *stgi;
+
+    stream_groups = av_realloc_array(s->stream_groups, s->nb_stream_groups + 1,
+                                     sizeof(*stream_groups));
+    if (!stream_groups)
+        return NULL;
+    s->stream_groups = stream_groups;
+
+    stgi = av_mallocz(sizeof(*stgi));
+    if (!stgi)
+        return NULL;
+    stg = &stgi->pub;
+
+    stg->av_class = &stream_group_class;
+    av_opt_set_defaults(stg);
+    stg->type = type;
+    switch (type) {
+    // Structs in the union are allocated here
+    default:
+        goto fail;
+    }
+
+    if (options) {
+        if (av_opt_set_dict2(stg, options, AV_OPT_SEARCH_CHILDREN))
+            goto fail;
+    }
+
+    stgi->fmtctx = s;
+    stg->index   = s->nb_stream_groups;
+
+    s->stream_groups[s->nb_stream_groups++] = stg;
+
+    return stg;
+fail:
+    ff_free_stream_group(&stg);
+    return NULL;
+}
+
+static int stream_group_add_stream(AVStreamGroup *stg, AVStream *st)
+{
+    AVStream **streams = av_realloc_array(stg->streams, stg->nb_streams + 1,
+                                          sizeof(*stg->streams));
+    if (!streams)
+        return AVERROR(ENOMEM);
+
+    stg->streams = streams;
+    stg->streams[stg->nb_streams++] = st;
+
+    return 0;
+}
+
+int avformat_stream_group_add_stream(AVStreamGroup *stg, AVStream *st)
+{
+    const FFStreamGroup *stgi = cffstreamgroup(stg);
+    const FFStream *sti = cffstream(st);
+
+    if (stgi->fmtctx != sti->fmtctx)
+        return AVERROR(EINVAL);
+
+    for (int i = 0; i < stg->nb_streams; i++)
+        if (stg->streams[i]->index == st->index)
+            return AVERROR(EEXIST);
+
+    return stream_group_add_stream(stg, st);
+}
+
 static int option_is_disposition(const AVOption *opt)
 {
     return opt->type == AV_OPT_TYPE_CONST &&
-- 
2.42.1



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