[FFmpeg-devel] [PATCH] libavformat/matroskaenc: Add WebM DASH support
Vignesh Venkatasubramanian
vigneshv at google.com
Tue May 13 19:07:12 CEST 2014
On Tue, May 13, 2014 at 6:08 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Mon, May 12, 2014 at 11:25:08PM -0700, Vignesh Venkatasubramanian wrote:
>> On Thu, May 8, 2014 at 10:11 AM, Vignesh Venkatasubramanian
>> <vigneshv at google.com> wrote:
>> > On Wed, May 7, 2014 at 3:37 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> >> On Wed, May 07, 2014 at 02:32:26PM -0700, Vignesh Venkatasubramanian wrote:
>> >>> On Wed, May 7, 2014 at 1:40 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> >>> > On Wed, May 07, 2014 at 09:46:40AM -0700, Vignesh Venkatasubramanian wrote:
>> >>> >> WebM DASH specification [1] requires the Clusters and Cues to be output in a
>> >>> >> specific way. Adding a flag to matroskaenc that will enable support for
>> >>> >> creating WebM/Mkv files conforming to the WebM DASH specification.
>> >>> >>
>> >>> >> [1] http://wiki.webmproject.org/adaptive-streaming/webm-dash-specification
>> >>> >>
>> >>> >> Signed-off-by: Vignesh Venkatasubramanian <vigneshv at google.com>
>> >>> >> ---
>> >>> >> libavformat/matroskaenc.c | 68 ++++++++++++++++++++++++++++++++++-------------
>> >>> >> 1 file changed, 50 insertions(+), 18 deletions(-)
>> >>> >>
>> >>> >> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
>> >>> >> index e5e6116..3cf6e73 100644
>> >>> >> --- a/libavformat/matroskaenc.c
>> >>> >> +++ b/libavformat/matroskaenc.c
>> >>> >> @@ -70,6 +70,7 @@ typedef struct mkv_seekhead {
>> >>> >>
>> >>> >> typedef struct {
>> >>> >> uint64_t pts;
>> >>> >> + int stream_idx;
>> >>> >> int tracknum;
>> >>> >> int64_t cluster_pos; ///< file offset of the cluster containing the block
>> >>> >> int64_t relative_pos; ///< relative offset from the position of the cluster containing the block
>> >>> >> @@ -114,6 +115,8 @@ typedef struct MatroskaMuxContext {
>> >>> >> int cluster_size_limit;
>> >>> >> int64_t cues_pos;
>> >>> >> int64_t cluster_time_limit;
>> >>> >> + int is_dash;
>> >>> >> + int dash_track_number;
>> >>> >>
>> >>> >> uint32_t chapter_id_offset;
>> >>> >> int wrote_chapters;
>> >>> >> @@ -399,8 +402,8 @@ static mkv_cues * mkv_start_cues(int64_t segment_offset)
>> >>> >> return cues;
>> >>> >> }
>> >>> >>
>> >>> >> -static int mkv_add_cuepoint(mkv_cues *cues, int stream, int64_t ts, int64_t cluster_pos, int64_t relative_pos,
>> >>> >> - int64_t duration)
>> >>> >> +static int mkv_add_cuepoint(mkv_cues *cues, int stream, int tracknum, int64_t ts,
>> >>> >> + int64_t cluster_pos, int64_t relative_pos, int64_t duration)
>> >>> >> {
>> >>> >> mkv_cuepoint *entries = cues->entries;
>> >>> >>
>> >>> >> @@ -413,7 +416,8 @@ static int mkv_add_cuepoint(mkv_cues *cues, int stream, int64_t ts, int64_t clus
>> >>> >> cues->entries = entries;
>> >>> >>
>> >>> >> cues->entries[cues->num_entries].pts = ts;
>> >>> >> - cues->entries[cues->num_entries].tracknum = stream + 1;
>> >>> >> + cues->entries[cues->num_entries].stream_idx = stream;
>> >>> >> + cues->entries[cues->num_entries].tracknum = tracknum;
>> >>> >> cues->entries[cues->num_entries].cluster_pos = cluster_pos - cues->segment_offset;
>> >>> >> cues->entries[cues->num_entries].relative_pos = relative_pos;
>> >>> >> cues->entries[cues->num_entries++].duration = duration;
>> >>> >> @@ -443,7 +447,7 @@ static int64_t mkv_write_cues(AVIOContext *pb, mkv_cues *cues, mkv_track *tracks
>> >>> >> for (j = 0; j < num_tracks; j++)
>> >>> >> tracks[j].has_cue = 0;
>> >>> >> for (j = 0; j < cues->num_entries - i && entry[j].pts == pts; j++) {
>> >>> >> - int tracknum = entry[j].tracknum - 1;
>> >>> >> + int tracknum = entry[j].stream_idx;
>> >>> >> av_assert0(tracknum>=0 && tracknum<num_tracks);
>> >>> >> if (tracks[tracknum].has_cue)
>> >>> >> continue;
>> >>> >> @@ -646,8 +650,10 @@ static int mkv_write_tracks(AVFormatContext *s)
>> >>> >> get_aac_sample_rates(s, codec, &sample_rate, &output_sample_rate);
>> >>> >>
>> >>> >> track = start_ebml_master(pb, MATROSKA_ID_TRACKENTRY, 0);
>> >>> >> - put_ebml_uint (pb, MATROSKA_ID_TRACKNUMBER , i + 1);
>> >>> >> - put_ebml_uint (pb, MATROSKA_ID_TRACKUID , i + 1);
>> >>> >> + put_ebml_uint (pb, MATROSKA_ID_TRACKNUMBER,
>> >>> >> + mkv->is_dash ? mkv->dash_track_number : i + 1);
>> >>> >> + put_ebml_uint (pb, MATROSKA_ID_TRACKUID,
>> >>> >> + mkv->is_dash ? mkv->dash_track_number : i + 1);
>> >>> >> put_ebml_uint (pb, MATROSKA_ID_TRACKFLAGLACING , 0); // no lacing (yet)
>> >>> >>
>> >>> >> if ((tag = av_dict_get(st->metadata, "title", NULL, 0)))
>> >>> >> @@ -1425,7 +1431,8 @@ static void mkv_write_block(AVFormatContext *s, AVIOContext *pb,
>> >>> >>
>> >>> >> put_ebml_id(pb, blockid);
>> >>> >> put_ebml_num(pb, size+4, 0);
>> >>> >> - avio_w8(pb, 0x80 | (pkt->stream_index + 1)); // this assumes stream_index is less than 126
>> >>> >> + // this assumes stream_index is less than 126
>> >>> >> + avio_w8(pb, 0x80 | (mkv->is_dash ? mkv->dash_track_number : (pkt->stream_index + 1)));
>> >>> >> avio_wb16(pb, ts - mkv->cluster_pts);
>> >>> >> avio_w8(pb, flags);
>> >>> >> avio_write(pb, data + offset, size);
>> >>> >> @@ -1539,7 +1546,7 @@ static void mkv_flush_dynbuf(AVFormatContext *s)
>> >>> >> mkv->dyn_bc = NULL;
>> >>> >> }
>> >>> >>
>> >>> >> -static int mkv_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
>> >>> >> +static int mkv_write_packet_internal(AVFormatContext *s, AVPacket *pkt, int add_cue)
>> >>> >> {
>> >>> >> MatroskaMuxContext *mkv = s->priv_data;
>> >>> >> AVIOContext *pb = s->pb;
>> >>> >> @@ -1596,8 +1603,13 @@ static int mkv_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
>> >>> >> end_ebml_master(pb, blockgroup);
>> >>> >> }
>> >>> >>
>> >>> >> - if ((codec->codec_type == AVMEDIA_TYPE_VIDEO && keyframe) || codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
>> >>> >> - ret = mkv_add_cuepoint(mkv->cues, pkt->stream_index, ts, mkv->cluster_pos, relative_packet_pos,
>> >>> >> + if ((codec->codec_type == AVMEDIA_TYPE_VIDEO && keyframe) ||
>> >>> >> + codec->codec_type == AVMEDIA_TYPE_SUBTITLE ||
>> >>> >> + add_cue) {
>> >>> >> + ret = mkv_add_cuepoint(mkv->cues,
>> >>> >> + pkt->stream_index,
>> >>> >> + mkv->is_dash ? mkv->dash_track_number : pkt->stream_index + 1,
>> >>> >> + ts, mkv->cluster_pos, relative_packet_pos,
>> >>> >> codec->codec_type == AVMEDIA_TYPE_SUBTITLE ? duration : -1);
>> >>> >> if (ret < 0) return ret;
>> >>> >> }
>> >>> >> @@ -1615,6 +1627,7 @@ static int mkv_write_packet(AVFormatContext *s, AVPacket *pkt)
>> >>> >> int64_t cluster_time;
>> >>> >> AVIOContext *pb;
>> >>> >> int ret;
>> >>> >> + int start_new_cluster;
>> >>> >>
>> >>> >> if (mkv->tracks[pkt->stream_index].write_dts)
>> >>> >> cluster_time = pkt->dts - mkv->cluster_pts;
>> >>> >> @@ -1632,11 +1645,26 @@ static int mkv_write_packet(AVFormatContext *s, AVPacket *pkt)
>> >>> >> cluster_size = avio_tell(pb);
>> >>> >> }
>> >>> >>
>> >>> >> - if (mkv->cluster_pos != -1 &&
>> >>> >> - (cluster_size > mkv->cluster_size_limit ||
>> >>> >> - cluster_time > mkv->cluster_time_limit ||
>> >>> >> - (codec_type == AVMEDIA_TYPE_VIDEO && keyframe &&
>> >>> >> - cluster_size > 4 * 1024))) {
>> >>> >> + if (mkv->is_dash && codec_type == AVMEDIA_TYPE_VIDEO) {
>> >>> >> + // WebM DASH specification states that the first block of every cluster
>> >>> >> + // has to be a key frame. So for DASH video, we only create a cluster
>> >>> >> + // on seeing key frames.
>> >>> >
>> >>> >> + start_new_cluster = keyframe;
>> >>> >
>> >>> > is it intended to have 1 frame per cluster for intra only videos ?
>> >>>
>> >>> yes. but this only done when -dash parameter is explicitly set. so
>> >>> it's very unlikely that someone would want intra-only video for dash.
>> >>
>> >> Someone might already have a intra only video and want to transmit
>> >> it without reencoding or
>> >> a encoder might choose to encode multiple frames in a row to be
>> >> encoded as intra frames (for example in a very high motion scene)
>> >>
>> >>
>> >
>> > that looks like a valid use case. i will rather limit it by
>> > cluster_time_limit and force a keyframe with the encoder whenever a
>> > cluster is to be created. will update the patch soon.
>> >
>>
>> on second thought, using cluster_time_limit as a sole factor will
>> produce incorrect DASH files in case of remuxing without encoding (as
>> there might not be a key frame when the cluster_time_limit is
>> reached).
>>
>> so there are two options here. one is to use cluster_time_limit as the
>> sole factor (and force keyframes with the encode whenever the cluster
>> time limit is reached). this will create incorrect files in case of
>> remux. the second option is to use the existing patch. this will
>> always produce correct DASH files (although it will be inefficient in
>> the case of intra-only files).
>>
>> thoughts?
>
> I guess we should get it working & compliant first before trying to
> make it behave better for less common cases
> as this seems not as trivial and obvious to fix as it seemed first
>
ok fine.
> did you had a chance to look at a fate test for this ?
working on it. will update the patch when i have it.
>
> [...]
> --
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> The educated differ from the uneducated as much as the living from the
> dead. -- Aristotle
>
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--
Vignesh
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