[FFmpeg-devel] [PATCH v2] avformat/mov: add interleaved_read option

[FFmpeg-devel] [PATCH v2] avformat/mov: add interleaved_read option

[Zhao Zhili]

From: Zhao Zhili <zhilizhao@tencent.com>

For bad interleaved files, manually interleave multiple tracks at the
demuxer level can trigger seeking back and forth, which can be
dramatically slow depending on the protocol. Demuxer level interleave
can be useless sometimes, e.g., reading mp4 via http and then
transcoding/remux to DASH. Disable this option when you don't need the
demuxer level interleave, and want to avoid the IO penalizes.

This issue is well known. Two samples can be found at here
http://ffmpeg.org/pipermail/ffmpeg-devel/2022-December/304951.html

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
---
 doc/demuxers.texi     | 6 ++++++
 libavformat/isom.h    | 1 +
 libavformat/mov.c     | 5 ++++-
 libavformat/version.h | 2 +-
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/doc/demuxers.texi b/doc/demuxers.texi
index 2d33b47a56..1b65332224 100644
--- a/doc/demuxers.texi
+++ b/doc/demuxers.texi
@@ -779,6 +779,12 @@ cast to int32 are used to adjust onward dts.
 
 Unit is the track time scale. Range is 0 to UINT_MAX. Default is @code{UINT_MAX - 48000*10} which allows upto
 a 10 second dts correction for 48 kHz audio streams while accommodating 99.9% of @code{uint32} range.
+
+@item interleaved_read
+Interleaved read between multiple tracks, enabled by default. For bad interleaved files, manually interleave multiple
+tracks at the demuxer level can trigger seeking back and forth, which can be dramatically slow depending on the
+protocol. Disable this option when you don't need the demuxer level interleave, and want to avoid the IO penalizes.
+
 @end table
 
 @subsection Audible AAX
diff --git a/libavformat/isom.h b/libavformat/isom.h
index 4b1cd42f0f..3d375d7a46 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -327,6 +327,7 @@ typedef struct MOVContext {
         int64_t extent_offset;
     } *avif_info;
     int avif_info_size;
+    int interleaved_read;
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);
diff --git a/libavformat/mov.c b/libavformat/mov.c
index aa1d9e4ccc..8ad5f0b646 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -8780,6 +8780,8 @@ static AVIndexEntry *mov_find_next_sample(AVFormatContext *s, AVStream **st)
     AVIndexEntry *sample = NULL;
     int64_t best_dts = INT64_MAX;
     int i;
+    MOVContext *mov = s->priv_data;
+    int no_interleave = !mov->interleaved_read || !(s->pb->seekable & AVIO_SEEKABLE_NORMAL);
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *avst = s->streams[i];
         FFStream *const avsti = ffstream(avst);
@@ -8788,7 +8790,7 @@ static AVIndexEntry *mov_find_next_sample(AVFormatContext *s, AVStream **st)
             AVIndexEntry *current_sample = &avsti->index_entries[msc->current_sample];
             int64_t dts = av_rescale(current_sample->timestamp, AV_TIME_BASE, msc->time_scale);
             av_log(s, AV_LOG_TRACE, "stream %d, sample %d, dts %"PRId64"\n", i, msc->current_sample, dts);
-            if (!sample || (!(s->pb->seekable & AVIO_SEEKABLE_NORMAL) && current_sample->pos < sample->pos) ||
+            if (!sample || (no_interleave && current_sample->pos < sample->pos) ||
                 ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) &&
                  ((msc->pb != s->pb && dts < best_dts) || (msc->pb == s->pb && dts != AV_NOPTS_VALUE &&
                  ((FFABS(best_dts - dts) <= AV_TIME_BASE && current_sample->pos < sample->pos) ||
@@ -9282,6 +9284,7 @@ static const AVOption mov_options[] = {
     { "enable_drefs", "Enable external track support.", OFFSET(enable_drefs), AV_OPT_TYPE_BOOL,
         {.i64 = 0}, 0, 1, FLAGS },
     { "max_stts_delta", "treat offsets above this value as invalid", OFFSET(max_stts_delta), AV_OPT_TYPE_INT, {.i64 = UINT_MAX-48000*10 }, 0, UINT_MAX, .flags = AV_OPT_FLAG_DECODING_PARAM },
+    { "interleaved_read", "Manually interleave between multiple tracks", OFFSET(interleaved_read), AV_OPT_TYPE_BOOL, {.i64 = 1 }, 0, 1, .flags = AV_OPT_FLAG_DECODING_PARAM },
 
     { NULL },
 };
diff --git a/libavformat/version.h b/libavformat/version.h
index 1055753772..695e17ed7f 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -32,7 +32,7 @@
 #include "version_major.h"
 
 #define LIBAVFORMAT_VERSION_MINOR  11
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \
-- 
2.34.1

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Re: [FFmpeg-devel] [PATCH v2] avformat/mov: add interleaved_read option

[Derek Buitenhuis]

Hi,

On 9/10/2023 6:51 AM, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> For bad interleaved files, manually interleave multiple tracks at the
> demuxer level can trigger seeking back and forth, which can be
> dramatically slow depending on the protocol. Demuxer level interleave
> can be useless sometimes, e.g., reading mp4 via http and then
> transcoding/remux to DASH. Disable this option when you don't need the
> demuxer level interleave, and want to avoid the IO penalizes.
> 
> This issue is well known. Two samples can be found at here
> http://ffmpeg.org/pipermail/ffmpeg-devel/2022-December/304951.html

Sorry for the slow reply.
> +@item interleaved_read
> +Interleaved read between multiple tracks, enabled by default. For bad interleaved files, manually interleave multiple
> +tracks at the demuxer level can trigger seeking back and forth, which can be dramatically slow depending on the
> +protocol. Disable this option when you don't need the demuxer level interleave, and want to avoid the IO penalizes.

I would write it with a description of what it does, rather than what disabling it would do,
maybe something like:

    Interleave packets from multiple tracks at demuxer level. For badly interleaved files, this prevents playback issues
    caused by large gaps between packets in different tracks, as MOV/MP4 do not have packet placement requirements.
    However, this can cause excessive seeking on very badly interleaved files, due to seeking between tracks, so disabling
    it may prevent I/O issues, at the expense of playback.

Again, apologies for forgetting to reply.

- Derek
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