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demux: change backward-overlap to keyframe ranges instead of packets 

This seems more useful in general. This change also happens to fix a
miscounting of preroll packets when some of them were "rounded" away,
and which could make it stuck.

Also a simple intra-refresh encode with x264 (and muxed to mkv by it)
seems to work now. I guess I misinterpreted earlier results.
This commit is contained in:
wm4 2019-05-24 19:17:31 +02:00
parent ba95a0b573
commit 085c7106b9
2 changed files with 41 additions and 39 deletions
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10
DOCS/man/options.rst
View File

@ -543,7 +543,8 @@ Playback Control
accept suffixes such as ``KiB`` and ``MiB``.
``--video-backward-overlap=<auto|number>``, ``--audio-backward-overlap=<auto|number>``
Number of overlapping packets to use for backward decoding (default: auto).
Number of overlapping keyframe ranges to use for backward decoding (default:
auto) ("keyframe" to be understood as in the mpv/ffmpeg specific meaning).
Backward decoding works by forward decoding in small steps. Some codecs
cannot restart decoding from any packet (even if it's marked as seek point),
which becomes noticeable with backward decoding (in theory this is a problem
@ -554,10 +555,9 @@ Playback Control
discard the output. This option controls how many packets to feed. The
``auto`` choice is currently hardcoded to 1 for audio, and 0 for video.
``--video-backward-overlap`` was intended to handle intra-refresh video, but
which does not work since libavcodec silently drops frames even with
``--vd-lavc-show-all``, and it's too messy to accurately guess which frames
have been dropped.
``--video-backward-overlap`` can potentially handle intra-refresh video,
depending on the exact conditions. You may have to use the
``--vd-lavc-show-all`` option as well.
``--demuxer-backward-playback-step=<seconds>``
Number of seconds the demuxer should seek back to get new packets during

70
demux/demux.c
View File

@ -1329,31 +1329,46 @@ static void find_backward_restart_pos(struct demux_stream *ds)
// Find where to restart demuxing. It's usually the last keyframe packet
// before restart_pos, but might be up to back_preroll packets earlier.
struct demux_packet *last_keyframe = NULL;
struct demux_packet *target = NULL;
// Keep this packet at back_preroll packets before last_keyframe.
struct demux_packet *pre_packet = ds->reader_head;
int pre_packet_offset = ds->back_preroll;
struct demux_packet *last_keyframe = NULL; // keyframe before back_restart
// (Normally, we'd just iterate backwards, but no back links.)
for (struct demux_packet *cur = ds->reader_head;
cur != back_restart;
cur = cur->next)
{
if (cur->keyframe) {
last_keyframe = cur;
target = pre_packet;
}
if (pre_packet_offset) {
pre_packet_offset--;
} else {
pre_packet = pre_packet->next;
int num_kf = 0;
struct demux_packet *pre_1 = NULL; // idiotic "optimization" for preroll=1
for (struct demux_packet *dp = first; dp != back_restart; dp = dp->next) {
if (dp->keyframe) {
num_kf++;
pre_1 = last_keyframe; // 1 keyframe before final last_keyframe
last_keyframe = dp;
}
}
if (!last_keyframe) {
struct demux_packet *target = NULL; // resume pos
int got_preroll = 0; // nr. of keyframes, incl. target, excl. last_keyframe
if (ds->back_preroll == 0) {
target = last_keyframe;
} else if (ds->back_preroll == 1) {
target = pre_1;
if (!target && ds->queue->is_bof)
target = last_keyframe;
got_preroll = target == pre_1 ? 1 : 0;
} else if (num_kf > ds->back_preroll || ds->queue->is_bof) {
got_preroll = ds->back_preroll;
if (num_kf <= ds->back_preroll && ds->queue->is_bof)
got_preroll = MPMAX(0, num_kf - 1);
int cur_kf = 0;
for (struct demux_packet *dp = first; dp != back_restart; dp = dp->next) {
if (dp->keyframe) {
cur_kf++;
if (num_kf - cur_kf == got_preroll) {
target = dp;
break;
}
}
}
}
if (!target) {
// Note: assume this holds true. You could think of various reasons why
// this might break.
if (ds->queue->is_bof) {
@ -1368,19 +1383,6 @@ static void find_backward_restart_pos(struct demux_stream *ds)
goto resume_earlier;
}
int got_preroll = 0;
for (struct demux_packet *cur = target;
cur != last_keyframe;
cur = cur->next)
got_preroll++;
if (got_preroll < ds->back_preroll && !ds->queue->is_bof)
goto resume_earlier;
// (Round preroll down to 0 in the worst case.)
while (!target->keyframe)
target = target->next;
// Skip reader_head from previous keyframe to current one.
// Or if preroll is involved, the first preroll packet.
while (ds->reader_head != target) {
@ -2299,7 +2301,7 @@ static int dequeue_packet(struct demux_stream *ds, struct demux_packet **res)
pkt->next = NULL;
if (ds->in->back_demuxing) {
if (ds->back_range_min)
if (ds->back_range_min && pkt->keyframe)
ds->back_range_min -= 1;
if (ds->back_range_min) {
pkt->back_preroll = true;