@@ -4483,8 +4483,7 @@ static int mov_write_tfxd_tag(AVIOContext *pb, MOVTrack *track)
avio_write(pb, uuid, sizeof(uuid));
avio_w8(pb, 1);
avio_wb24(pb, 0);
- avio_wb64(pb, track->start_dts + track->frag_start +
- track->cluster[0].cts);
+ avio_wb64(pb, track->cluster[0].dts + track->cluster[0].cts);
avio_wb64(pb, track->end_pts -
(track->cluster[0].dts + track->cluster[0].cts));
@@ -4563,8 +4562,7 @@ static int mov_add_tfra_entries(AVIOContext *pb, MOVMuxContext *mov, int tracks,
info->size = size;
// Try to recreate the original pts for the first packet
// from the fields we have stored
- info->time = track->start_dts + track->frag_start +
- track->cluster[0].cts;
+ info->time = track->cluster[0].dts + track->cluster[0].cts;
info->duration = track->end_pts -
(track->cluster[0].dts + track->cluster[0].cts);
// If the pts is less than zero, we will have trimmed
@@ -4602,7 +4600,7 @@ static int mov_write_tfdt_tag(AVIOContext *pb, MOVTrack *track)
ffio_wfourcc(pb, "tfdt");
avio_w8(pb, 1); /* version */
avio_wb24(pb, 0);
- avio_wb64(pb, track->frag_start);
+ avio_wb64(pb, track->cluster[0].dts - track->start_dts);
return update_size(pb, pos);
}
@@ -4679,8 +4677,7 @@ static int mov_write_sidx_tag(AVIOContext *pb,
if (track->entry) {
entries = 1;
- presentation_time = track->start_dts + track->frag_start +
- track->cluster[0].cts;
+ presentation_time = track->cluster[0].dts + track->cluster[0].cts;
duration = track->end_pts -
(track->cluster[0].dts + track->cluster[0].cts);
starts_with_SAP = track->cluster[0].flags & MOV_SYNC_SAMPLE;
@@ -5359,10 +5356,6 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
mov->moov_written = 1;
mov->mdat_size = 0;
for (i = 0; i < mov->nb_streams; i++) {
- if (mov->tracks[i].entry)
- mov->tracks[i].frag_start += mov->tracks[i].start_dts +
- mov->tracks[i].track_duration -
- mov->tracks[i].cluster[0].dts;
mov->tracks[i].entry = 0;
mov->tracks[i].end_reliable = 0;
}
@@ -5416,11 +5409,7 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
MOVTrack *track = &mov->tracks[i];
int buf_size, write_moof = 1, moof_tracks = -1;
uint8_t *buf;
- int64_t duration = 0;
- if (track->entry)
- duration = track->start_dts + track->track_duration -
- track->cluster[0].dts;
if (mov->flags & FF_MOV_FLAG_SEPARATE_MOOF) {
if (!track->entry)
continue;
@@ -5440,8 +5429,6 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
ffio_wfourcc(s->pb, "mdat");
}
- if (track->entry)
- track->frag_start += duration;
track->entry = 0;
track->entries_flushed = 0;
track->end_reliable = 0;
@@ -5760,7 +5747,6 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
/* New fragment, but discontinuous from previous fragments.
* Pretend the duration sum of the earlier fragments is
* pkt->dts - trk->start_dts. */
- trk->frag_start = pkt->dts - trk->start_dts;
trk->end_pts = AV_NOPTS_VALUE;
trk->frag_discont = 0;
}
@@ -5782,12 +5768,10 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
/* Pretend the whole stream started at pts=0, with earlier fragments
* already written. If the stream started at pts=0, the duration sum
* of earlier fragments would have been pkt->pts. */
- trk->frag_start = pkt->pts;
trk->start_dts = pkt->dts - pkt->pts;
} else {
/* Pretend the whole stream started at dts=0, with earlier fragments
* already written, with a duration summing up to pkt->dts. */
- trk->frag_start = pkt->dts;
trk->start_dts = 0;
}
trk->frag_discont = 0;
@@ -138,7 +138,6 @@ typedef struct MOVTrack {
AVIOContext *mdat_buf;
int64_t data_offset;
- int64_t frag_start;
int frag_discont;
int entries_flushed;
"frag_start" is redundant, and every occurance can be replaced with cluster[0].dts - start_dts The proof of no behaviour changes: (All line number below is based on commit bff7d662d728) "frag_start" is read at 4 place (with all possible call stacks): mov_write_packet ... mov_flush_fragment mov_write_moof_tag mov_write_moof_tag_internal mov_write_traf_tag mov_write_tfxd_tag (#1) mov_write_tfdt_tag (#2) mov_add_tfra_entries (#3) mov_write_sidx_tags mov_write_sidx_tag (#4) mov_write_trailer mov_auto_flush_fragment mov_flush_fragment ... (#1 #2 #3 #4) mov_write_sidx_tags mov_write_sidx_tag (#4) shift_data compute_sidx_size get_sidx_size mov_write_sidx_tags mov_write_sidx_tag (#4) All read happens in "mov_write_trailer" and "mov_write_moof_tag". So we need to prove no behaviour change in these two functions. Condition 1: for every track that have "trk->entry == 0", trk->frag_start == trk->track_duration. Condition 2: for every track that have "trk->entry > 0", trk->frag_start == trk->cluster[0].dts - trk->start_dts. Definition 1: "Before flush" means just before the invocation of "mov_flush_fragment", except for the auto-flush case in "mov_write_single_packet", which means before L5934. Lemma 1: If Condition 1 & 2 is true before flush, Condition 1 & 2 is still true after "mov_flush_fragment" returns. Proof: No update to the tracks that have "trk->entry == 0" before flushing, so we only consider tracks that have "trk->entry > 0": Case 1: !moov_written and moov will be written in this iteration trk->entry = 0 L5366 trk->frag_start == trk->cluster[0].dts - trk->start_dts Lemma condition trk->frag_start += trk->start_dts + trk->track_duration - trk->cluster[0].dts; L5363 So trk->entry == 0 && trk->frag_start == trk->track_duration Case 2: !moov_written and moov will NOT be written in this iteration nothing changed Case 3: moov_written trk->entry = 0 L5445 trk->frag_start == trk->cluster[0].dts - trk->start_dts Lemma condition trk->frag_start += trk->start_dts + trk->track_duration - trk->cluster[0].dts; L5444 So trk->entry == 0 && trk->frag_start == trk->track_duration Note that trk->track_duration may be updated for the tracks that have "trk->entry > 0" (mov_write_moov_tag will update track_duration of "tmcd" track, but it must have 1 entry). But in all case, trk->frag_start is also updated to consider the new value. Lemma 2: If Condition 1 & 2 is true before "ff_mov_write_packet" invocation, Condition 1 & 2 is still true after it returns. Proof: Only the track corresponding to the pkt is updated, and no update to relevant variables if trk->entry > 0 before invocation. So we only need to prove "trk->frag_start == trk->cluster[0].dts - trk->start_dts" after trk->entry increase from 0 to 1. Case 1: trk->start_dts == AV_NOPTS_VALUE Case 1.1: trk->frag_discont && use_editlist trk->cluster[0].dts = pkt->dts at L5741 trk->frag_start = pkt->pts at L5785 trk->start_dts = pkt->dts - pkt->pts at L5786 So trk->frag_start == trk->cluster[0].dts - trk->start_dts Case 1.2: trk->frag_discont && !use_editlist trk->cluster[0].dts = pkt->dts at L5741 trk->frag_start = pkt->dts at L5790 trk->start_dts = 0 at L5791 So trk->frag_start == trk->cluster[0].dts - trk->start_dts Case 1.3: !trk->frag_discont trk->cluster[0].dts = pkt->dts at L5741 trk->frag_start = 0 init trk->start_dts = pkt->dts at L5779 So trk->frag_start == trk->cluster[0].dts - trk->start_dts Case 2: trk->start_dts != AV_NOPTS_VALUE Case 2.1: trk->frag_discont trk->cluster[0].dts = pkt->dts at L5741 trk->frag_start = pkt->dts - trk->start_dts at L5763 So trk->frag_start == trk->cluster[0].dts - trk->start_dts Case 2.2: !trk->frag_discont trk->cluster[0].dts = trk->start_dts + trk->track_duration at L5749 trk->track_duration == trk->frag_start Lemma condition So trk->frag_start == trk->cluster[0].dts - trk->start_dts Lemma 3: Condition 1 & 2 is true in all case before and after "ff_mov_write_packet" invocation, before flush and after "mov_flush_fragment" returns. Proof: All updates to relevant variable happen either in "ff_mov_write_packet", or during flush. And Condition 1 & 2 is true initially. So with lemma 1 & 2, we can prove this use induction. Noticed that all read of "frag_start" only happen in "trk->entry > 0" branch. Now we need to prove Condition 2 is true before each read. Because no update to variables relevant to Condition 2 between "before flush" and "mov_write_moof_tag" invocation, we can conclude Condition 2 is true before every invocation of "mov_write_moof_tag". No behaviour change in "mov_write_moof_tag" is proved. In "mov_write_trailer", No update to relevant variables after the last flush and before the invocation of "mov_write_sidx_tag". So no behaviour change to "mov_write_trailer" is proved. Q.E.D. Signed-off-by: Hu Weiwen <sehuww@mail.scut.edu.cn> --- Hopefully this patch and/or the proof can make the code more clear to future readers. Thank you for reading this long proof. I'm doing something like this for the first time. Please kindly point it out if you find anything incorrect or confusing. libavformat/movenc.c | 24 ++++-------------------- libavformat/movenc.h | 1 - 2 files changed, 4 insertions(+), 21 deletions(-) -- 2.25.1