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matroska: Provide audio lead-in for some lossy formats

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Various audio formats require an audio lead-in to decode it properly.
Most parsers would take care of it, but when a container like matroska is
involved, the demuxer handles the seeking and without its own lead-in
handling would never even pass the lead-in data to the parser.
This commit provides an initial implementation of that for audio/mpeg,
audio/x-ac3 and audio/x-eac3 by calculating the worst case lead-in time
needed from known samplerate, potential lead-in frames need and the
maximum blocksize possible for the format (as we don't parse that out
exactly in matroskademux) and seeking that much earlier in case of
accurate seeks. This is especially important for NLE use-cases with GES.

If accurate seeking to a position that happens to have a video keyframe,
it'll go back to the previous keyframe than needed, but with typical
video files that's the best we can do anyway without falling back to
scanning the clusters, as typically only keyframes are indexed in
Cueing Data.
If the media doesn't have a CUE, then we bisect for the cluster to seek
to with the same modified time as well in case of accurate seeking,
ensuring sufficient lead-in. This code path is typically hit only with
(suboptimal) audio-only matroska files, e.g. when created with ffmpeg,
which doesn't add a CUE for audio-only mkv muxing.
This commit is contained in:
Mart Raudsepp 2019-07-10 22:07:05 +03:00 committed by Olivier Crête
parent 1c5c90ea23
commit 67958ccce8
2 changed files with 44 additions and 6 deletions
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49
gst/matroska/matroska-demux.c
View file

@ -171,7 +171,7 @@ static GstCaps *gst_matroska_demux_video_caps (GstMatroskaTrackVideoContext
gchar ** codec_name, guint32 * riff_fourcc);
static GstCaps *gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext
* audiocontext, const gchar * codec_id, guint8 * data, guint size,
gchar ** codec_name, guint16 * riff_audio_fmt);
gchar ** codec_name, guint16 * riff_audio_fmt, GstClockTime * lead_in_ts);
static GstCaps
* gst_matroska_demux_subtitle_caps (GstMatroskaTrackSubtitleContext *
subtitlecontext, const gchar * codec_id, gpointer data, guint size);
@ -339,6 +339,7 @@ gst_matroska_demux_reset (GstElement * element)
demux->segment_seqnum = 0;
demux->requested_seek_time = GST_CLOCK_TIME_NONE;
demux->seek_offset = -1;
demux->audio_lead_in_ts = 0;
demux->building_index = FALSE;
if (demux->seek_event) {
gst_event_unref (demux->seek_event);
@ -1512,12 +1513,18 @@ gst_matroska_demux_parse_stream (GstMatroskaDemux * demux, GstEbmlRead * ebml,
}
case GST_MATROSKA_TRACK_TYPE_AUDIO:{
GstClockTime lead_in_ts = 0;
GstMatroskaTrackAudioContext *audiocontext =
(GstMatroskaTrackAudioContext *) context;
caps = gst_matroska_demux_audio_caps (audiocontext,
context->codec_id, context->codec_priv, context->codec_priv_size,
&codec, &riff_audio_fmt);
&codec, &riff_audio_fmt, &lead_in_ts);
if (lead_in_ts > demux->audio_lead_in_ts) {
demux->audio_lead_in_ts = lead_in_ts;
GST_DEBUG_OBJECT (demux, "Increased audio lead-in to %" GST_TIME_FORMAT,
GST_TIME_ARGS (lead_in_ts));
}
if (codec) {
gst_tag_list_add (context->tags, GST_TAG_MERGE_REPLACE,
@ -2734,11 +2741,12 @@ gst_matroska_demux_handle_seek_event (GstMatroskaDemux * demux,
GstSeekFlags flags;
GstSeekType cur_type, stop_type;
GstFormat format;
gboolean flush, keyunit, before, after, snap_next;
gboolean flush, keyunit, before, after, accurate, snap_next;
gdouble rate;
gint64 cur, stop;
GstMatroskaTrackContext *track = NULL;
GstSegment seeksegment = { 0, };
guint64 seekpos;
gboolean update = TRUE;
gboolean pad_locked = FALSE;
guint32 seqnum;
@ -2806,6 +2814,7 @@ gst_matroska_demux_handle_seek_event (GstMatroskaDemux * demux,
keyunit = ! !(flags & GST_SEEK_FLAG_KEY_UNIT);
after = ! !(flags & GST_SEEK_FLAG_SNAP_AFTER);
before = ! !(flags & GST_SEEK_FLAG_SNAP_BEFORE);
accurate = ! !(flags & GST_SEEK_FLAG_ACCURATE);
/* always do full update if flushing,
* otherwise problems might arise downstream with missing keyframes etc */
@ -2821,9 +2830,15 @@ gst_matroska_demux_handle_seek_event (GstMatroskaDemux * demux,
snap_dir = snap_next ? GST_SEARCH_MODE_AFTER : GST_SEARCH_MODE_BEFORE;
GST_OBJECT_LOCK (demux);
seekpos = seeksegment.position;
if (accurate) {
seekpos -= MIN (seeksegment.position, demux->audio_lead_in_ts);
}
track = gst_matroska_read_common_get_seek_track (&demux->common, track);
if ((entry = gst_matroska_read_common_do_index_seek (&demux->common, track,
seeksegment.position, &demux->seek_index, &demux->seek_entry,
seekpos, &demux->seek_index, &demux->seek_entry,
snap_dir)) == NULL) {
/* pull mode without index can scan later on */
if (demux->streaming) {
@ -2890,7 +2905,7 @@ next:
gst_event_set_seqnum (flush_event, seqnum);
gst_pad_push_event (demux->common.sinkpad, flush_event);
}
entry = gst_matroska_demux_search_pos (demux, seeksegment.position);
entry = gst_matroska_demux_search_pos (demux, seekpos);
/* keep local copy */
if (entry) {
scan_entry = *entry;
@ -6606,10 +6621,16 @@ round_up_pow2 (guint n)
static GstCaps *
gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
audiocontext, const gchar * codec_id, guint8 * data, guint size,
gchar ** codec_name, guint16 * riff_audio_fmt)
gchar ** codec_name, guint16 * riff_audio_fmt, GstClockTime * lead_in_ts)
{
GstMatroskaTrackContext *context = (GstMatroskaTrackContext *) audiocontext;
GstCaps *caps = NULL;
guint lead_in = 0;
/* Max potential blocksize causing the longest possible lead_in_ts need, as
* we don't have the exact number parsed out here */
guint max_blocksize = 0;
/* Original samplerate before SBR multiplications, as parsers would use */
guint rate = audiocontext->samplerate;
g_assert (audiocontext != NULL);
g_assert (codec_name != NULL);
@ -6640,6 +6661,8 @@ gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
else
layer = 3;
lead_in = 30; /* Could mp2 need as much too? */
max_blocksize = 1152;
caps = gst_caps_new_simple ("audio/mpeg",
"mpegversion", G_TYPE_INT, 1, "layer", G_TYPE_INT, layer, NULL);
*codec_name = g_strdup_printf ("MPEG-1 layer %d", layer);
@ -6687,11 +6710,15 @@ gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
context->alignment = round_up_pow2 (context->alignment);
} else if (!strncmp (codec_id, GST_MATROSKA_CODEC_ID_AUDIO_AC3,
strlen (GST_MATROSKA_CODEC_ID_AUDIO_AC3))) {
lead_in = 2;
max_blocksize = 1536;
caps = gst_caps_new_simple ("audio/x-ac3",
"framed", G_TYPE_BOOLEAN, TRUE, NULL);
*codec_name = g_strdup ("AC-3 audio");
} else if (!strncmp (codec_id, GST_MATROSKA_CODEC_ID_AUDIO_EAC3,
strlen (GST_MATROSKA_CODEC_ID_AUDIO_EAC3))) {
lead_in = 2;
max_blocksize = 1536;
caps = gst_caps_new_simple ("audio/x-eac3",
"framed", G_TYPE_BOOLEAN, TRUE, NULL);
*codec_name = g_strdup ("E-AC-3 audio");
@ -6751,6 +6778,7 @@ gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
samplerate =
audiocontext->samplerate == 0 ? 48000 : audiocontext->samplerate;
rate = samplerate;
channels = audiocontext->channels == 0 ? 2 : audiocontext->channels;
if (channels == 1) {
streams = 1;
@ -6833,6 +6861,8 @@ gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
/* assume SBR if samplerate <= 24kHz */
if (obj_type == 5 || (freq_index >= 6 && freq_index != 15) ||
(context->codec_priv_size == (5 + explicit_freq_bytes))) {
/* TODO: Commonly aacparse will reset the rate in caps to
* non-multiplied - which one is correct? */
audiocontext->samplerate *= 2;
}
} else {
@ -6890,6 +6920,8 @@ gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
}
if (priv) {
lead_in = 2;
max_blocksize = 1024;
caps = gst_caps_new_simple ("audio/mpeg",
"mpegversion", G_TYPE_INT, mpegversion,
"framed", G_TYPE_BOOLEAN, TRUE,
@ -6992,6 +7024,11 @@ gst_matroska_demux_audio_caps (GstMatroskaTrackAudioContext *
caps = gst_caps_simplify (caps);
}
if (lead_in_ts && lead_in && max_blocksize && rate) {
*lead_in_ts =
gst_util_uint64_scale (GST_SECOND, max_blocksize * lead_in, rate);
}
return caps;
}

1
gst/matroska/matroska-demux.h
View file

@ -90,6 +90,7 @@ typedef struct _GstMatroskaDemux {
guint64 next_cluster_offset;
GstClockTime requested_seek_time;
guint64 seek_offset;
GstClockTime audio_lead_in_ts;
/* alternative duration; optionally obtained from last cluster */
guint64 last_cluster_offset;