DASH and Variable framerate

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DASH and Variable framerate

Alfred E. Heggestad
Hi,

I am wondering if DASH muxer supports variable framerate.


What I have seen is that DASH and HLS behaves differently
regarding variable framerate input.


   muxer:               format:   audio delay:

   DASH:                m4s       yes
   DASH w HLS playlist: m4s       yes
   HLS muxer:           mpegts    no


in m4s the audio and video track is stored in separate .m4s files.
after some time they become out of sync.

in mpegts the audio/video track is stored in the same .ts file.
no issues with a/v sync here


The ffmpeg command is used with RTMP as input:


$ ffmpeg -listen 1 -i rtmp://127.0.0.1:1935/foo \
     -c:v copy \
     -c:a copy \
     \
     -f dash -remove_at_exit false playlist.mpd


any feedback is appreciated.




/alfred
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Re: DASH and Variable framerate

Moritz Barsnick
On Thu, Aug 06, 2020 at 15:00:55 +0200, Alfred E. Heggestad wrote:
> I am wondering if DASH muxer supports variable framerate.
[...]
> What I have seen is that DASH and HLS behaves differently
> regarding variable framerate input.
>    muxer:               format:   audio delay:
>
>    DASH:                m4s       yes
>    DASH w HLS playlist: m4s       yes
>    HLS muxer:           mpegts    no

I suspect this is due to the fact that ffmpeg does not handle variable
framerate in MOV/MP4 well (which m4s is a variant of, IIUC).

> in m4s the audio and video track is stored in separate .m4s files.
> after some time they become out of sync.

I don't think the separate files are the issue. HLS can also separate
video and audio into separate files, as far as I remember.

Cheers,
Moritz
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Re: DASH and Variable framerate

Alfred E. Heggestad


On 07/08/2020 13:25, Moritz Barsnick wrote:

> On Thu, Aug 06, 2020 at 15:00:55 +0200, Alfred E. Heggestad wrote:
>> I am wondering if DASH muxer supports variable framerate.
> [...]
>> What I have seen is that DASH and HLS behaves differently
>> regarding variable framerate input.
>>     muxer:               format:   audio delay:
>>
>>     DASH:                m4s       yes
>>     DASH w HLS playlist: m4s       yes
>>     HLS muxer:           mpegts    no
>
> I suspect this is due to the fact that ffmpeg does not handle variable
> framerate in MOV/MP4 well (which m4s is a variant of, IIUC).
>

Thanks for the answer. Yes m4s is fragmented MP4.

This also seems to match my observations.


/alfred

>> in m4s the audio and video track is stored in separate .m4s files.
>> after some time they become out of sync.
>
> I don't think the separate files are the issue. HLS can also separate
> video and audio into separate files, as far as I remember.
>
> Cheers,
> Moritz
> _______________________________________________
> ffmpeg-user mailing list
> [hidden email]
> https://ffmpeg.org/mailman/listinfo/ffmpeg-user
>
> To unsubscribe, visit link above, or email
> [hidden email] with subject "unsubscribe".
>
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