No EXT-X-MEDIA-SEQUENCE in HLS playlist

[Aleksey Ivanov]

Hello.

I use the packager to generate HLS for live stream.

For test purposes I use FFmpeg to generate a stream.

First I run Shaka in Docker:

packager \

  'input=udp://0.0.0.0:5004,stream=video,init_segment=hls/video_init.mp4,segment_template=hls/video_$Number$.ts,playlist_name=video.m3u8' \

  'input=udp://0.0.0.0:5004,stream=audio,init_segment=hls/audio_init.mp4,segment_template=hls/audio_$Number$.ts,playlist_name=audio.m3u8' \

  --hls_master_playlist_output hls/playlist.m3u8 --hls_playlist_type LIVE

Then I run FFmpeg on host machine:

ffmpeg \
  -f lavfi -re -i "testsrc=duration=-1:size=1280x720:rate=30" \

  -f lavfi -re -i "sine=f=50:beep_factor=6" \

  -pix_fmt yuv420p \

  -c:v libx264 -preset:v ultrafast -profile:v high -level 3.1 -tune:v zerolatency -r 30 -g 60 -sc_threshold 0 \

  -c:a libfdk_aac -preset:a ultrafast \

  -f mpegts udp://$(docker-machine ip default):5004

Unfortunately, when I try to play those files with Shaka Player I got the following error:

Shaka Error MANIFEST.HLS_MEDIA_SEQUENCE_REQUIRED_IN_LIVE_STREAMS ()

As far as I can see from Apple docs (Live Playlist (Sliding Window) section):

For live sessions, the index file is updated by removing media URIs from the file as new media files are created and made available.

My playlists look like this:

hls/playlist.m3u8

#EXTM3U

## Generated with https://github.com/google/shaka-packager version e97c893-release

#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio",NAME="stream_0",URI="audio.m3u8"

#EXT-X-STREAM-INF:BANDWIDTH=532398,CODECS="avc1.42c01f,mp4a.40.2",RESOLUTION=1280x720,AUDIO="audio"

video.m3u8

hls/video.m3u8

#EXTM3U

#EXT-X-VERSION:6

## Generated with https://github.com/google/shaka-packager version e97c893-release

#EXT-X-TARGETDURATION:11

#EXT-X-MAP:URI="video_init.mp4"

#EXTINF:10.000,

video_1.ts

#EXTINF:10.000,

video_2.ts

#EXTINF:10.000,

video_3.ts

#EXTINF:10.000,

video_4.ts

#EXTINF:10.000,

video_5.ts

#EXTINF:10.000,

video_6.ts

#EXTINF:10.000,

video_7.ts

#EXTINF:10.000,

video_8.ts

#EXTINF:10.000,

video_9.ts

#EXTINF:10.000,

video_10.ts

#EXTINF:10.000,

video_11.ts

#EXTINF:10.000,
...

I have read from the packager documentation that:

Packager does not support removing old segments internally. The user is responsible for setting up a cron job to do so.

But I think it is related to removing files itself.
As I understand the packager should remove some segments from playlist and increment EXT-X-MEDIA-SEQUENCE tag.

There is a code related to that, but unfortunately I am not able to understand it. In which cases we would get into that else branch?

So, my playlists is just getting longer and there is EXT-X-MEDIA-SEQUENCE tag in there.

Could you please tell me to figure it out?
It there is anything I could do to add EXT-X-MEDIA-SEQUENCE to playlist?
Is it a bug in the packager or it is me missing something?

Thank you.

[KongQun Yang]

Hi Aleksey,

Shaka Packager does generate EXT-X-MEDIA-SEQUENCE, but only when it is not 0: https://github.com/google/shaka-packager/blob/master/packager/hls/base/media_playlist.cc#L91. The tag will be generated when EXT-X-MEDIA-SEQUENCE becomes non-zero, i.e. when playlists update.

According to HLS spec https://tools.ietf.org/html/draft-pantos-http-live-streaming-23#section-4.3.3.2:

   If the Media Playlist file does not contain an EXT-X-MEDIA-SEQUENCE
   tag then the Media Sequence Number of the first Media Segment in the
   Media Playlist SHALL be considered to be 0.  A client MUST NOT assume
   that segments with the same Media Sequence Number in different Media
   Playlists contain matching content - see Section 6.3.2.

+Joey, does Shaka Player require EXT-X-MEDIA-SEQUENCE to be present for live playlist? This does not seem to be correct.

-- KongQun Yang (KQ)

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[Aleksey Ivanov]

Thank you KQ,

Yes, I saw the code:

if (media_sequence_number > 0) {

        base::StringAppendF(&header, "#EXT-X-MEDIA-SEQUENCE:%d\n",

                            media_sequence_number);

      }

And it can become non-zero only here.
So, we need num_segments_removed to be greater than zero too.
But how could we achieve that? 

As I wrote above in my case no segments were removed, they were only appended to a playlist.

The specification you linked is related to client-side behaviour, right?

[Joey Parrish]

I suppose that's a player bug.  Please file here: https://github.com/google/shaka-player/issues/new

It should be pretty easy to fix.

-- KongQun Yang (KQ)

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[KongQun Yang]

Hi Aleksey, 

See my replies inline.

-- KongQun Yang (KQ)

On Tue, Dec 12, 2017 at 9:56 AM, Aleksey Ivanov <iale...@gmail.com> wrote:

Thank you KQ,

Yes, I saw the code:

if (media_sequence_number > 0) {

        base::StringAppendF(&header, "#EXT-X-MEDIA-SEQUENCE:%d\n",

                            media_sequence_number);

      }

And it can become non-zero only here.
So, we need num_segments_removed to be greater than zero too.
But how could we achieve that? 

It happens when buffer shifts. The default "--time_shift_buffer_depth" is 30 minutes. You can adjust it, for example, set it to 60, i.e. 60 seconds. You should be able to see the sequence number updated every 60 seconds.

 

As I wrote above in my case no segments were removed, they were only appended to a playlist.

The specification you linked is related to client-side behaviour, right?

Yes. 

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[Aleksey Ivanov]

Thank you KQ, 

I use --time_shift_buffer_depth 60, it does the trick!

It would be nice to document this option for HLS, since now packager --help only prints info about it in "Flags from ../../packager/app/mpd_flags.cc:" section.
What do you think?

Joey, thanks, I will report a bug.

[KongQun Yang]

-- KongQun Yang (KQ)

On Tue, Dec 12, 2017 at 12:19 PM, Aleksey Ivanov <iale...@gmail.com> wrote:

Thank you KQ, 

I use --time_shift_buffer_depth 60, it does the trick!

It would be nice to document this option for HLS, since now packager --help only prints info about it in "Flags from ../../packager/app/mpd_flags.cc:" section.
What do you think?

Yes, that should be fixed. Filed an issue to track it: https://github.com/google/shaka-packager/issues/304. 

Joey, thanks, I will report a bug.

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