From 2e174354805ea220b6a57f6b8755347c7f240077 Mon Sep 17 00:00:00 2001 From: Matthieu Bouron Date: Fri, 30 Oct 2020 15:38:51 +0100 Subject: avformat/mov: adjust skip_samples according to seek timestamp Currently skip_samples is set to start_pad if sample_time is lesser or equal to 0. This can cause issues if the stream starts with packets that have negative pts. Calling avformat_seek_file() with ts set to 0 on such streams makes the mov demuxer return the right corresponding packets (near the 0 timestamp) but set skip_samples to start_pad which is incorrect as the audio decoder will discard the returned samples according to skip_samples from the first packet it receives (which has its timestamp near 0). For example, considering the following audio stream with start_pad=1344: [PKT pts=-1344] [PKT pts=-320] [PKT pts=704] [PKT pts=1728] [...] Calling avformat_seek_file() with ts=0 makes the next call to av_read_frame() return the packet with pts=-320 and a skip samples side data set to 1344 (start_pad). This makes the audio decoder incorrectly discard (1344 - 320) samples. This commit makes the move demuxer adjust skip_samples according to the stream start_pad, seek timestamp and first sample timestamp. The above example will now result in av_read_frame() still returning the packet with pts=-320 but with a skip samples side data set to 320 (src_pad - (seek_timestamp - first_timestamp)). This makes the audio decoder only discard 320 samples (from pts=-320 to pts=0). Signed-off-by: Marton Balint --- libavformat/mov.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) (limited to 'libavformat/mov.c') diff --git a/libavformat/mov.c b/libavformat/mov.c index c6a2d9c388..3215b53636 100644 --- a/libavformat/mov.c +++ b/libavformat/mov.c @@ -8122,6 +8122,22 @@ static int mov_seek_stream(AVFormatContext *s, AVStream *st, int64_t timestamp, return sample; } +static int64_t mov_get_skip_samples(AVStream *st, int sample) +{ + MOVStreamContext *sc = st->priv_data; + int64_t first_ts = st->internal->index_entries[0].timestamp; + int64_t ts = st->internal->index_entries[sample].timestamp; + int64_t off; + + if (st->codecpar->codec_type != AVMEDIA_TYPE_AUDIO) + return 0; + + /* compute skip samples according to stream start_pad, seek ts and first ts */ + off = av_rescale_q(ts - first_ts, st->time_base, + (AVRational){1, st->codecpar->sample_rate}); + return FFMAX(sc->start_pad - off, 0); +} + static int mov_read_seek(AVFormatContext *s, int stream_index, int64_t sample_time, int flags) { MOVContext *mc = s->priv_data; @@ -8140,18 +8156,19 @@ static int mov_read_seek(AVFormatContext *s, int stream_index, int64_t sample_ti if (mc->seek_individually) { /* adjust seek timestamp to found sample timestamp */ int64_t seek_timestamp = st->internal->index_entries[sample].timestamp; + st->internal->skip_samples = mov_get_skip_samples(st, sample); for (i = 0; i < s->nb_streams; i++) { int64_t timestamp; - MOVStreamContext *sc = s->streams[i]->priv_data; st = s->streams[i]; - st->internal->skip_samples = (sample_time <= 0) ? sc->start_pad : 0; if (stream_index == i) continue; timestamp = av_rescale_q(seek_timestamp, s->streams[stream_index]->time_base, st->time_base); - mov_seek_stream(s, st, timestamp, flags); + sample = mov_seek_stream(s, st, timestamp, flags); + if (sample >= 0) + st->internal->skip_samples = mov_get_skip_samples(st, sample); } } else { for (i = 0; i < s->nb_streams; i++) { -- cgit v1.2.3