[vlc-commits] demux: mp4: save track start point

[Francois Cartegnie]

vlc | branch: master | Francois Cartegnie <fcvlcdev at free.fr> | Mon Feb  8 20:40:50 2021 +0100| [ddd59a84895203bd3a84726a47d5bc2255137d68] | committer: Francois Cartegnie

demux: mp4: save track start point

> http://git.videolan.org/gitweb.cgi/vlc.git/?a=commit;h=ddd59a84895203bd3a84726a47d5bc2255137d68
---

 modules/demux/mp4/mp4.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 modules/demux/mp4/mp4.h |  2 ++
 2 files changed, 51 insertions(+)

diff --git a/modules/demux/mp4/mp4.c b/modules/demux/mp4/mp4.c
index d982590cdf..78b8b47b7a 100644
--- a/modules/demux/mp4/mp4.c
+++ b/modules/demux/mp4/mp4.c
@@ -344,6 +344,20 @@ static es_out_id_t * MP4_CreateES( es_out_t *out, const es_format_t *p_fmt,
     return p_es;
 }
 
+static const mp4_chunk_t * MP4_TrackChunkForSample( const mp4_track_t *p_track,
+                                                    uint32_t i_sample )
+{
+    if( i_sample >= p_track->i_sample_count )
+        return NULL;
+    for( uint32_t i=0; i<p_track->i_chunk_count; i++ )
+    {
+        if( i_sample >= p_track->chunk[i].i_sample_first &&
+            i_sample - p_track->chunk[i].i_sample_first < p_track->chunk[i].i_sample_count )
+            return &p_track->chunk[i];
+    }
+    return NULL;
+}
+
 static stime_t MP4_ChunkGetSampleDTS( const mp4_chunk_t *p_chunk,
                                       uint32_t i_sample )
 {
@@ -3325,6 +3339,40 @@ static int TrackGotoChunkSample( demux_t *p_demux, mp4_track_t *p_track,
     return p_track->b_selected ? VLC_SUCCESS : VLC_EGENERIC;
 }
 
+static void TrackUpdateStarttimes( mp4_track_t *p_track )
+{
+    assert(p_track->i_chunk < p_track->i_chunk_count);
+
+    p_track->i_start_dts = p_track->i_next_dts;
+    p_track->i_start_delta = p_track->i_next_delta;
+
+    /* Probe the 16 first B frames */
+    const mp4_chunk_t *p_chunk = &p_track->chunk[p_track->i_chunk];
+    if( p_chunk->i_entries_pts )
+    {
+        for( uint32_t i=1; i<16; i++ )
+        {
+            uint32_t i_nextsample = p_track->i_sample + i;
+            const mp4_chunk_t *ck = MP4_TrackChunkForSample( p_track, i_nextsample );
+            if(!ck)
+                break;
+            stime_t pts;
+            stime_t dts = pts = MP4_ChunkGetSampleDTS( ck, i_nextsample - ck->i_sample_first );
+            stime_t delta = UNKNOWN_DELTA;
+            if( MP4_ChunkGetSampleCTSDelta( ck, i_nextsample - ck->i_sample_first, &delta ) )
+                pts += delta;
+            stime_t lowest = p_track->i_start_dts;
+            if( p_track->i_start_delta != UNKNOWN_DELTA )
+                lowest += p_track->i_start_delta;
+            if( pts < lowest )
+            {
+                p_track->i_start_dts = dts;
+                p_track->i_start_delta = delta;
+            }
+        }
+    }
+}
+
 static void TrackUpdateSampleAndTimes( mp4_track_t *p_track )
 {
     const mp4_chunk_t *p_chunk = &p_track->chunk[p_track->i_chunk];
@@ -3696,6 +3744,7 @@ static int MP4_TrackSeek( demux_t *p_demux, mp4_track_t *p_track,
     {
         p_track->b_selected = true;
         TrackUpdateSampleAndTimes( p_track );
+        TrackUpdateStarttimes( p_track );
     }
 
     return p_track->b_selected ? VLC_SUCCESS : VLC_EGENERIC;
diff --git a/modules/demux/mp4/mp4.h b/modules/demux/mp4/mp4.h
index 640861b687..b05d81a044 100644
--- a/modules/demux/mp4/mp4.h
+++ b/modules/demux/mp4/mp4.h
@@ -128,7 +128,9 @@ typedef struct
     int64_t         i_elst_time;    /* current elst start time (in movie time scale)*/
     const MP4_Box_t *p_elst;        /* elst (could be NULL) */
 
+    uint32_t         i_start_delta;
     uint32_t         i_next_delta;
+    stime_t          i_start_dts;
     stime_t          i_next_dts;
     /* give the next sample to read, i_chunk is to find quickly where
       the sample is located */