movenc: Add an option for enabling negative CTS offsets

This reduces the need for an edit list; streams that start with
e.g. dts=-1, pts=0 can be encoded as dts=0, pts=0 (which is valid
in mov/mp4) by shifting the dts values of all packets forward.
This avoids the need for edit lists for such streams (while they
still are needed for audio streams with encoder delay).

This eases conformance with the DASH-IF interoperability guidelines.

Signed-off-by: Martin Storsjö <[email protected]>

1 files changed, 24 insertions, 4 deletions

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 840190dbfa..356d1d6b71 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -62,6 +62,7 @@ static const AVOption options[] = {
     { "delay_moov", "Delay writing the initial moov until the first fragment is cut, or until the first fragment flush", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_DELAY_MOOV}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "global_sidx", "Write a global sidx index at the start of the file", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_GLOBAL_SIDX}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "skip_trailer", "Skip writing the mfra/tfra/mfro trailer for fragmented files", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_SKIP_TRAILER}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
+    { "negative_cts_offsets", "Use negative CTS offsets (reducing the need for edit lists)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     FF_RTP_FLAG_OPTS(MOVMuxContext, rtp_flags),
     { "skip_iods", "Skip writing iods atom.", offsetof(MOVMuxContext, iods_skip), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, AV_OPT_FLAG_ENCODING_PARAM},
     { "iods_audio_profile", "iods audio profile atom.", offsetof(MOVMuxContext, iods_audio_profile), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 255, AV_OPT_FLAG_ENCODING_PARAM},
@@ -1163,8 +1164,9 @@ static int mov_write_stsd_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *tra
     return update_size(pb, pos);
 }
 
-static int mov_write_ctts_tag(AVIOContext *pb, MOVTrack *track)
+static int mov_write_ctts_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *track)
 {
+    MOVMuxContext *mov = s->priv_data;
     MOVStts *ctts_entries;
     uint32_t entries = 0;
     uint32_t atom_size;
@@ -1188,7 +1190,11 @@ static int mov_write_ctts_tag(AVIOContext *pb, MOVTrack *track)
     atom_size = 16 + (entries * 8);
     avio_wb32(pb, atom_size); /* size */
     ffio_wfourcc(pb, "ctts");
-    avio_wb32(pb, 0); /* version & flags */
+    if (mov->flags & FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS)
+        avio_w8(pb, 1); /* version */
+    else
+        avio_w8(pb, 0); /* version */
+    avio_wb24(pb, 0); /* flags */
     avio_wb32(pb, entries); /* entry count */
     for (i = 0; i < entries; i++) {
         avio_wb32(pb, ctts_entries[i].count);
@@ -1273,7 +1279,7 @@ static int mov_write_stbl_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *tra
         mov_write_stss_tag(pb, track, MOV_PARTIAL_SYNC_SAMPLE);
     if (track->par->codec_type == AVMEDIA_TYPE_VIDEO &&
         track->flags & MOV_TRACK_CTTS && track->entry)
-        mov_write_ctts_tag(pb, track);
+        mov_write_ctts_tag(s, pb, track);
     mov_write_stsc_tag(pb, track);
     mov_write_stsz_tag(pb, track);
     mov_write_stco_tag(pb, track);
@@ -2594,7 +2600,10 @@ static int mov_write_trun_tag(AVIOContext *pb, MOVMuxContext *mov,
 
     avio_wb32(pb, 0); /* size placeholder */
     ffio_wfourcc(pb, "trun");
-    avio_w8(pb, 0); /* version */
+    if (mov->flags & FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS)
+        avio_w8(pb, 1); /* version */
+    else
+        avio_w8(pb, 0); /* version */
     avio_wb24(pb, flags);
 
     avio_wb32(pb, end - first); /* sample count */
@@ -3040,6 +3049,8 @@ static int mov_write_ftyp_tag(AVIOContext *pb, AVFormatContext *s)
         ffio_wfourcc(pb, "MSNV");
     else if (mov->mode == MODE_MP4 && mov->flags & FF_MOV_FLAG_DEFAULT_BASE_MOOF)
         ffio_wfourcc(pb, "iso5"); // Required when using default-base-is-moof
+    else if (mov->mode == MODE_MP4 && mov->flags & FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS)
+        ffio_wfourcc(pb, "iso4");
     else if (mov->mode == MODE_MP4)
         ffio_wfourcc(pb, "isom");
     else if (mov->mode == MODE_IPOD)
@@ -3288,6 +3299,8 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
         if (!track->end_reliable) {
             AVPacket pkt;
             if (!ff_interleaved_peek(s, i, &pkt, 1)) {
+                if (track->dts_shift != AV_NOPTS_VALUE)
+                    pkt.dts += track->dts_shift;
                 track->track_duration = pkt.dts - track->start_dts;
                 if (pkt.pts != AV_NOPTS_VALUE)
                     track->end_pts = pkt.pts;
@@ -3729,6 +3742,12 @@ static int mov_write_packet(AVFormatContext *s, AVPacket *pkt)
             mov->flags &= ~FF_MOV_FLAG_FRAG_DISCONT;
         }
 
+        if (mov->flags & FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS) {
+            if (trk->dts_shift == AV_NOPTS_VALUE)
+                trk->dts_shift = pkt->pts - pkt->dts;
+            pkt->dts += trk->dts_shift;
+        }
+
         if (!pkt->size) {
             if (trk->start_dts == AV_NOPTS_VALUE && trk->frag_discont) {
                 trk->start_dts = pkt->dts;
@@ -4095,6 +4114,7 @@ static int mov_write_header(AVFormatContext *s)
         track->start_dts  = AV_NOPTS_VALUE;
         track->start_cts  = AV_NOPTS_VALUE;
         track->end_pts    = AV_NOPTS_VALUE;
+        track->dts_shift  = AV_NOPTS_VALUE;
         if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
             if (track->tag == MKTAG('m','x','3','p') || track->tag == MKTAG('m','x','3','n') ||
                 track->tag == MKTAG('m','x','4','p') || track->tag == MKTAG('m','x','4','n') ||