movenc: Add an option for skipping writing the mfra/tfra/mfro trailer

When writing a fragmented file, we by default write an index pointing
to all the fragments at the end of the file. This causes constantly
increasing memory usage during the muxing. For live streams, the
index might not be useful at all.

A similar fragment index is written (but at the start of the file) if
the global_sidx flag is set. If ism_lookahead is set, we need to keep
data about the last ism_lookahead+1 fragments.

If no fragment index is to be written, we don't need to store information
about all fragments, avoiding increasing the memory consumption
linearly with the muxing runtime.

This fixes out of memory situations with long live mp4 streams.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/movenc.c

@@ -60,6 +60,7 @@ static const AVOption options[] = {
     { "frag_discont", "Signal that the next fragment is discontinuous from earlier ones", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_FRAG_DISCONT}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "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" },
     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},
@@ -2732,6 +2733,20 @@ static int mov_add_tfra_entries(AVIOContext *pb, MOVMuxContext *mov, int tracks,
     return 0;
 }
 
+static void mov_prune_frag_info(MOVMuxContext *mov, int tracks, int max)
+{
+    int i;
+    for (i = 0; i < mov->nb_streams; i++) {
+        MOVTrack *track = &mov->tracks[i];
+        if ((tracks >= 0 && i != tracks) || !track->entry)
+            continue;
+        if (track->nb_frag_info > max) {
+            memmove(track->frag_info, track->frag_info + (track->nb_frag_info - max), max * sizeof(*track->frag_info));
+            track->nb_frag_info = max;
+        }
+    }
+}
+
 static int mov_write_tfdt_tag(AVIOContext *pb, MOVTrack *track)
 {
     int64_t pos = avio_tell(pb);
@@ -2917,8 +2932,16 @@ static int mov_write_moof_tag(AVIOContext *pb, MOVMuxContext *mov, int tracks,
     if (mov->flags & FF_MOV_FLAG_DASH && !(mov->flags & FF_MOV_FLAG_GLOBAL_SIDX))
         mov_write_sidx_tags(pb, mov, tracks, moof_size + 8 + mdat_size);
 
-    if ((ret = mov_add_tfra_entries(pb, mov, tracks, moof_size + 8 + mdat_size)) < 0)
-        return ret;
+    if (mov->flags & FF_MOV_FLAG_GLOBAL_SIDX ||
+        !(mov->flags & FF_MOV_FLAG_SKIP_TRAILER) ||
+        mov->ism_lookahead) {
+        if ((ret = mov_add_tfra_entries(pb, mov, tracks, moof_size + 8 + mdat_size)) < 0)
+            return ret;
+        if (!(mov->flags & FF_MOV_FLAG_GLOBAL_SIDX) &&
+            mov->flags & FF_MOV_FLAG_SKIP_TRAILER) {
+            mov_prune_frag_info(mov, tracks, mov->ism_lookahead + 1);
+        }
+    }
 
     return mov_write_moof_tag_internal(pb, mov, tracks, moof_size);
 }
@@ -4389,7 +4412,7 @@ static int mov_write_trailer(AVFormatContext *s)
                 avio_write_marker(s->pb, AV_NOPTS_VALUE, AVIO_DATA_MARKER_TRAILER);
                 mov_write_mfra_tag(pb, mov);
             }
-        } else {
+        } else if (!(mov->flags & FF_MOV_FLAG_SKIP_TRAILER)) {
             avio_write_marker(s->pb, AV_NOPTS_VALUE, AVIO_DATA_MARKER_TRAILER);
             mov_write_mfra_tag(pb, mov);
         }

libavformat/movenc.h

@@ -194,6 +194,7 @@ typedef struct MOVMuxContext {
 #define FF_MOV_FLAG_FRAG_DISCONT          (1 << 12)
 #define FF_MOV_FLAG_DELAY_MOOV            (1 << 13)
 #define FF_MOV_FLAG_GLOBAL_SIDX           (1 << 14)
+#define FF_MOV_FLAG_SKIP_TRAILER          (1 << 15)
 
 int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt);