On Thu, 13 May 2021, Josh Allmann wrote:
Previously, one or the other would have been ignored, but not both. Since the probe terminates at three streams, it could exit prematurely if both data and subtitles are present along with slightly trailing media, usually video trailing audio.Trailing media is common in RTMP, and encoders write strange metadata. --- libavformat/flvdec.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c index 4b9f46902b..1be8d98618 100644 --- a/libavformat/flvdec.c +++ b/libavformat/flvdec.c @@ -134,18 +134,32 @@ static void add_keyframes_index(AVFormatContext *s) } } +static int is_ignorable(enum AVMediaType codec_type) +{ + switch(codec_type) { + case AVMEDIA_TYPE_SUBTITLE: + case AVMEDIA_TYPE_DATA: + return 1; + } + return 0; +} + static AVStream *create_stream(AVFormatContext *s, int codec_type) { + int streams_to_ignore = 0, nb_streams = 0; FLVContext *flv = s->priv_data; AVStream *st = avformat_new_stream(s, NULL); if (!st) return NULL; st->codecpar->codec_type = codec_type; - if (s->nb_streams>=3 ||( s->nb_streams==2 - && s->streams[0]->codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE - && s->streams[1]->codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE - && s->streams[0]->codecpar->codec_type != AVMEDIA_TYPE_DATA - && s->streams[1]->codecpar->codec_type != AVMEDIA_TYPE_DATA)) + + if (s->nb_streams >= 1) + streams_to_ignore += is_ignorable(s->streams[0]->codecpar->codec_type); + if (s->nb_streams >= 2) + streams_to_ignore += is_ignorable(s->streams[1]->codecpar->codec_type); + + nb_streams = s->nb_streams - streams_to_ignore; + if (nb_streams >= 2) s->ctx_flags &= ~AVFMTCTX_NOHEADER;
Overall, the idea of the patch seems sensible, but it could be done slightly differently...
Instead of explicitly inspecting streams [0] and [1], wouldn't it be more straightforward to just loop over all existing streams and count the ones where is_ignorable returns 0? Otherwise, if you'd have e.g. the streams {audio, data, subtitle}, you'd still end up with nb_streams = 2 which probably isn't what you meant?
Separately, it'd be great if you could, while touching this code, write some comments about what's happening here - it's rather non-obvious code (especially with the double negations, in clearing the NOHEADER flag, and what that flag implies).
// Martin _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
