[FFmpeg-devel] [PATCH 1/2 v2] movenc: Add an option for enabling negative CTS offsets
Jan Ekström
jeebjp at gmail.com
Tue Sep 26 02:48:27 EEST 2017
From: Martin Storsjö <martin at martin.st>
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 <martin at martin.st>
---
doc/muxers.texi | 2 ++
libavformat/movenc.c | 28 ++++++++++++++++++++++++----
libavformat/movenc.h | 2 ++
3 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/doc/muxers.texi b/doc/muxers.texi
index 36769b8c1a..312749942c 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -1055,6 +1055,8 @@ on the implicit end of the previous track fragment).
@item -write_tmcd
Specify @code{on} to force writing a timecode track, @code{off} to disable it
and @code{auto} to write a timecode track only for mov and mp4 output (default).
+ at item -movflags negative_cts_offsets
+Enables utilization of version 1 of the CTTS box, in which the CTS offsets can be negative. This enables the initial sample to have DTS/CTS of zero, and reduces the need for edit lists for some cases such as video tracks with B-frames. Additionally, eases conformance with the DASH-IF interoperability guidelines.
@end table
@subsection Example
diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 10b959ad02..917486384a 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -77,6 +77,7 @@ static const AVOption options[] = {
{ "write_gama", "Write deprecated gama atom", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_WRITE_GAMA}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
{ "use_metadata_tags", "Use mdta atom for metadata.", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_USE_MDTA}, 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_BOOL, {.i64 = 1}, 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},
@@ -2094,8 +2095,9 @@ static int mov_write_stsd_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContext
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;
@@ -2119,7 +2121,11 @@ 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);
@@ -2303,7 +2309,7 @@ static int mov_write_stbl_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContext
if (track->par->codec_type == AVMEDIA_TYPE_VIDEO &&
track->flags & MOV_TRACK_CTTS && track->entry) {
- if ((ret = mov_write_ctts_tag(pb, track)) < 0)
+ if ((ret = mov_write_ctts_tag(s, pb, track)) < 0)
return ret;
}
mov_write_stsc_tag(pb, track);
@@ -4044,7 +4050,10 @@ 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 */
@@ -4489,6 +4498,8 @@ 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)
@@ -4759,6 +4770,8 @@ 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;
@@ -5282,6 +5295,12 @@ static int mov_write_single_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 (trk->par->codec_id == AV_CODEC_ID_MP4ALS ||
trk->par->codec_id == AV_CODEC_ID_AAC ||
trk->par->codec_id == AV_CODEC_ID_FLAC) {
@@ -5922,6 +5941,7 @@ static int mov_init(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') ||
diff --git a/libavformat/movenc.h b/libavformat/movenc.h
index 4c4f3cdfc3..cc2a155d79 100644
--- a/libavformat/movenc.h
+++ b/libavformat/movenc.h
@@ -116,6 +116,7 @@ typedef struct MOVTrack {
int64_t start_cts;
int64_t end_pts;
int end_reliable;
+ int64_t dts_shift;
int hint_track; ///< the track that hints this track, -1 if no hint track is set
int src_track; ///< the track that this hint (or tmcd) track describes
@@ -241,6 +242,7 @@ typedef struct MOVMuxContext {
#define FF_MOV_FLAG_WRITE_GAMA (1 << 16)
#define FF_MOV_FLAG_USE_MDTA (1 << 17)
#define FF_MOV_FLAG_SKIP_TRAILER (1 << 18)
+#define FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS (1 << 19)
int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt);
--
2.13.5
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