On 3 Apr 2025, at 22:02, Dimitry Andric <dimi...@unified-streaming.com> wrote:
>
> When decoding fragmented MP4 files that have an empty stsc box, and
> instead contain sample description indexes in their tfhd boxes, the mov
> demuxer does not notify the decoder whenever the current sample
> description index changes. If the SPS or PPS changed sufficiently, this
> can lead to unexpected decoding errors.
>
> To fix this, in mov_finalize_packet(), when stsc_data is not available,
> use get_frag_stream_info_from_pkt() to get at the current fragment
> stream info, and retrieve the current sample description index from
> there. Then use that index in a similar manner as the stsc case.
>
> Signed-off-by: Dimitry Andric <dimi...@unified-streaming.com>
> ---
> libavformat/mov.c | 50 ++++++++++++++++++++++++++++-------------------
> 1 file changed, 30 insertions(+), 20 deletions(-)
>
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 452690090c..ead89192f4 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -10756,25 +10756,29 @@ static int mov_switch_root(AVFormatContext *s,
> int64_t target, int index)
> return 1;
> }
>
> -static int mov_change_extradata(AVStream *st, AVPacket *pkt)
> +static int mov_change_extradata(AVStream *st, AVPacket *pkt, int stsd_id)
> {
> MOVStreamContext *sc = st->priv_data;
> uint8_t *side, *extradata;
> int extradata_size;
>
> - /* Save the current index. */
> - sc->last_stsd_index = sc->stsc_data[sc->stsc_index].id - 1;
> + if (stsd_id > 0 &&
> + stsd_id - 1 < sc->stsd_count &&
> + stsd_id - 1 != sc->last_stsd_index) {
> + /* Save the current index. */
> + sc->last_stsd_index = stsd_id - 1;
>
> - /* Notify the decoder that extradata changed. */
> - extradata_size = sc->extradata_size[sc->last_stsd_index];
> - extradata = sc->extradata[sc->last_stsd_index];
> - if (st->discard != AVDISCARD_ALL && extradata_size > 0 && extradata) {
> - side = av_packet_new_side_data(pkt,
> - AV_PKT_DATA_NEW_EXTRADATA,
> - extradata_size);
> - if (!side)
> - return AVERROR(ENOMEM);
> - memcpy(side, extradata, extradata_size);
> + /* Notify the decoder that extradata changed. */
> + extradata_size = sc->extradata_size[sc->last_stsd_index];
> + extradata = sc->extradata[sc->last_stsd_index];
> + if (st->discard != AVDISCARD_ALL && extradata_size > 0 && extradata)
> {
> + side = av_packet_new_side_data(pkt,
> + AV_PKT_DATA_NEW_EXTRADATA,
> + extradata_size);
> + if (!side)
> + return AVERROR(ENOMEM);
> + memcpy(side, extradata, extradata_size);
> + }
> }
>
> return 0;
> @@ -10893,13 +10897,10 @@ static int mov_finalize_packet(AVFormatContext *s,
> AVStream *st, AVIndexEntry *s
>
> /* Multiple stsd handling. */
> if (sc->stsc_data) {
> - if (sc->stsc_data[sc->stsc_index].id > 0 &&
> - sc->stsc_data[sc->stsc_index].id - 1 < sc->stsd_count &&
> - sc->stsc_data[sc->stsc_index].id - 1 != sc->last_stsd_index) {
> - int ret = mov_change_extradata(st, pkt);
> - if (ret < 0)
> - return ret;
> - }
> + int stsd_id = sc->stsc_data[sc->stsc_index].id;
> + int ret = mov_change_extradata(st, pkt, stsd_id);
> + if (ret < 0)
> + return ret;
>
> /* Update the stsc index for the next sample */
> sc->stsc_sample++;
> @@ -10908,6 +10909,15 @@ static int mov_finalize_packet(AVFormatContext *s,
> AVStream *st, AVIndexEntry *s
> sc->stsc_index++;
> sc->stsc_sample = 0;
> }
> + } else {
> + MOVContext *mov = s->priv_data;
> + MOVFragmentStreamInfo *frag_stream_info =
> get_frag_stream_info_from_pkt(&mov->frag_index, pkt, sc->id);
> + if (frag_stream_info) {
> + int stsd_id = frag_stream_info->stsd_id;
> + int ret = mov_change_extradata(st, pkt, stsd_id);
> + if (ret < 0)
> + return ret;
> + }
> }
>
> return 0;
> --
> 2.43.0
>
Any comments on this patch?
-Dimitry
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