mov: Add option to keep exact packet sequence after seeking

The current behavior may produce a different sequence of packets
after seeking, compared to demuxing linearly from the beginning.
This is because the MOV demuxer seeks in each stream individually,
based on timestamp, which may set each stream at a slightly different
position than if the file would have been read sequentially.

This makes implementing certain operations, such as segmenting,
quite hard, and slower than need be.

Therefore, add an option which retains the same packet sequence
after seeking, as when a file is demuxed linearly.

libavformat/isom.h

@@ -186,6 +186,7 @@ typedef struct MOVContext {
     int chapter_track;
     int use_absolute_path;
     int ignore_editlist;
+    int seek_individually;
     int64_t next_root_atom; ///< offset of the next root atom
     int export_all;
     int export_xmp;

libavformat/mov.c

@@ -4325,8 +4325,8 @@ static int mov_seek_stream(AVFormatContext *s, AVStream *st, int64_t timestamp,
 
 static int mov_read_seek(AVFormatContext *s, int stream_index, int64_t sample_time, int flags)
 {
+    MOVContext *mc = s->priv_data;
     AVStream *st;
-    int64_t seek_timestamp, timestamp;
     int sample;
     int i;
 
@@ -4338,19 +4338,39 @@ static int mov_read_seek(AVFormatContext *s, int stream_index, int64_t sample_ti
     if (sample < 0)
         return sample;
 
-    /* adjust seek timestamp to found sample timestamp */
-    seek_timestamp = st->index_entries[sample].timestamp;
+    if (mc->seek_individually) {
+        /* adjust seek timestamp to found sample timestamp */
+        int64_t seek_timestamp = st->index_entries[sample].timestamp;
 
-    for (i = 0; i < s->nb_streams; i++) {
-        MOVStreamContext *sc = s->streams[i]->priv_data;
-        st = s->streams[i];
-        st->skip_samples = (sample_time <= 0) ? sc->start_pad : 0;
+        for (i = 0; i < s->nb_streams; i++) {
+            int64_t timestamp;
+            MOVStreamContext *sc = s->streams[i]->priv_data;
+            st = s->streams[i];
+            st->skip_samples = (sample_time <= 0) ? sc->start_pad : 0;
 
-        if (stream_index == i)
-            continue;
+            if (stream_index == i)
+                continue;
 
-        timestamp = av_rescale_q(seek_timestamp, s->streams[stream_index]->time_base, st->time_base);
-        mov_seek_stream(s, st, timestamp, flags);
+            timestamp = av_rescale_q(seek_timestamp, s->streams[stream_index]->time_base, st->time_base);
+            mov_seek_stream(s, st, timestamp, flags);
+        }
+    } else {
+        for (i = 0; i < s->nb_streams; i++) {
+            MOVStreamContext *sc;
+            st = s->streams[i];
+            sc = st->priv_data;
+            sc->current_sample = 0;
+        }
+        while (1) {
+            MOVStreamContext *sc;
+            AVIndexEntry *entry = mov_find_next_sample(s, &st);
+            if (!entry)
+                return AVERROR_INVALIDDATA;
+            sc = st->priv_data;
+            if (sc->ffindex == stream_index && sc->current_sample == sample)
+                break;
+            sc->current_sample++;
+        }
     }
     return 0;
 }
@@ -4362,6 +4382,10 @@ static const AVOption mov_options[] = {
         "allow using absolute path when opening alias, this is a possible security issue",
         OFFSET(use_absolute_path), FF_OPT_TYPE_INT, {.i64 = 0},
         0, 1, FLAGS},
+    {"seek_streams_individually",
+        "Seek each stream individually to the to the closest point",
+        OFFSET(seek_individually), AV_OPT_TYPE_INT, { .i64 = 1 },
+        0, 1, FLAGS},
     {"ignore_editlist", "", OFFSET(ignore_editlist), FF_OPT_TYPE_INT, {.i64 = 0},
         0, 1, FLAGS},
     {"use_mfra_for",

libavformat/version.h

@@ -30,8 +30,8 @@
 #include "libavutil/version.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 56
-#define LIBAVFORMAT_VERSION_MINOR  25
-#define LIBAVFORMAT_VERSION_MICRO 101
+#define LIBAVFORMAT_VERSION_MINOR  26
+#define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \