problems with webm support

[mstoykov]

I use tears of steel webm file as the test file (http://ftp.nluug.nl/pub/graphics/blender/demo/movies/ToS/tears_of_steel_1080p.webm) . Using it just like it is I get 404 and this in the logs

mkv_metadata_reader_read: truncated file (2) while sending to client, client: 172.17.0.1, server: , request: "GET /dash/tears_of_steel.webm/manifest.mpd HTTP/1.1", host: "1-1.b.cdn13.com" 

After some hours of trial and error I figured that the audio was the problem. Removing the audio yielded manifest with two segments with total length of 7 seconds although full 15 seconds were played by dash.js.

After some reencoding, looking up what was recommended around the issues and the web I used:

ffmpeg -i tears_of_steel.webm -t 30  -s 960x400 -c:v libvpx-vp9 -speed 2  -threads 4 -tile-columns 4 -frame-parallel 1 -auto-alt-ref 1 -lag-in-frames 25 -crf 20 -c:a libopus -b:a 64k -f webm 

The -t 30 -s 960x400 is to minimize the size of the encode time. With these options and practically anything else I tried with very little deviation (and not positive at that) I will get a manifest like

<?xml version="1.0"?>                                                                          
<MPD                                                                                           
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"                                      
    xmlns="urn:mpeg:dash:schema:mpd:2011"                                                      
    xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 http://standards.iso.org/ittf/PubliclyAvailableStandards/MPEG-DASH_schema_files/DASH-MPD.xsd"                                            
    type="static"                                                                              
    mediaPresentationDuration="PT30.006S"                                                      
    minBufferTime="PT10S"                                                                      
    profiles="urn:mpeg:dash:profile:isoff-main:2011">                                          
  <Period>                                                                                     
    <AdaptationSet                                                                             
        id="1"                                                                                 
        segmentAlignment="true"                                                                
        maxWidth="960"                                                                         
        maxHeight="400"                                                                        
        maxFrameRate="500/21">                                                                 
        <SegmentTemplate                                                                       
            timescale="1000"                                                                   
            media="fragment-$Number$-$RepresentationID$.webm"                                  
            initialization="init-$RepresentationID$.webm"                                      
            startNumber="1">                                                                   
            <SegmentTimeline>                                                                  
                <S d="5333"/>                                                                  
                <S d="1334"/>                                                                  
            </SegmentTimeline>                                                                 
        </SegmentTemplate>                                                                     
      <Representation                                                                          
          id="v1-x3"                                                                           
          mimeType="video/webm"                                                                
          codecs="vp9"                                                                         
          width="960"                                                                          
          height="400"                                                                         
          frameRate="500/21"                                                                   
          sar="1:1"                                                                            
          startWithSAP="1"                                                                     
          bandwidth="0">                                                                       
      </Representation>                                                                        
    </AdaptationSet>                                                                           
    <AdaptationSet                                                                             
        id="2"                                                                                 
        segmentAlignment="true">                                                               
      <AudioChannelConfiguration                                                               
          schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011"                 
          value="1"/>                                                                          
        <SegmentTemplate                                                                       
            timescale="1000"                                                                   
            media="fragment-$Number$-$RepresentationID$.webm"                                  
            initialization="init-$RepresentationID$.webm"                                      
            startNumber="1">                                                                   
            <SegmentTimeline>                                                                  
                <S d="3198"/>                                                                  
            </SegmentTimeline>                                                                 
        </SegmentTemplate>                                                                     
      <Representation                                                                          
          id="a1-x3"                                                                           
          mimeType="audio/webm"                                                                
          codecs="opus"                                                                        
          audioSamplingRate="48000"                                                            
          startWithSAP="1"                                                                     
          bandwidth="0">                                                                       
      </Representation>                                                                        
    </AdaptationSet>                                                                           
  </Period>                                                                                    
</MPD>               

which because of the single audio segment and it size will play for 3 seconds and stop, without the audio I would get the same behavior as before. Also I hit #780, but because the size of the video I just raised the value of vod_max_frames_size to 1024m,

If I change the container to mp4 add -strict -2 and change the audio codec to ac3, the generated manifest for the mp4 will be fine and playable (atleast for the 30 seconds, I am going to try the whole video soon)

I suppose I am doing something wrong. But no changes in the way I encode or the whether I use mkv or webm yielded a playable dash manifest. All the videos are playable from the same firefox I am testing the manifest, so they are not corrupted or something else that will make them unplayable

[erankor]

I checked this sample, there are 2 issues here -

1. It uses lacing for the audio frames, this is not supported.
2. There is an issue in the 9th video fragment - the validation performed by the module is too strict.

I created a quick hack for the second issue, and the video plays fine. A more elegant fix can probably be implemented quite easily, but considering the first issue and the fact MKV in general has been discontinued, I'm not sure it's worth the effort.

[mstoykov]

First thank you for the quick reply.

Could you propose how to (re)encode/mux the file in order for the current source to work?

The fix, even the hack one, would be greatly appreciated as even though MKV might be discontinued, which I am not aware of, webm seems to be doing good for itself.

[erankor]

Sorry, I meant 'discontinued in the context of this module', not the format as a whole :) Regarding lacing - you can probably repackage (without retranscoding) using ffmpeg - ffmpeg doesn't use lacing when encoding MKV. I'll check regarding the code fix

[mstoykov]

Is there any update on the fix? I would be happy with the quick hack as well :).

[erankor]

Sorry for the delay, I now pushed the change that I wrote shortly after you opened this issue - https://github.com/kaltura/nginx-vod-module/pull/867 What I didn't like about this change was that I had to apply it on 'simple block' element (it didn't work when I applied it only on 'cluster'). I wanted to dig deeper into it, but didn't get a chance to do it.

[mstoykov]

For me this fix did not change the returned playlist - I still get only around 3 seconds of playthrough. Maybe you missed some part of it ? I'm going to try some more encoding options to see if it will make a difference.

[jessp01]

Hi @MStoykov, any news on this? Thanks.

[tan-tan-kanarek]

+1