[FFmpeg-devel] Forward frame wall clock time from avdevice to HLS muxer

[Marton Balint]

On Wed, 26 Aug 2020, Andreas Rheinhardt wrote:

> Jesper Ek:
>> Hi,
>> 
>> I have implemented a libavdevice to capture audio and video from an AJA
>> Kona card (similar to decklink). I'm then using the HLS muxer to encode my
>> stream. Now I need the HLS EXT-X-PROGRAM-DATE-TIME tag to specify exactly
>> when the input source was recorded, so my plan is to forward the "wall
>> clock time" (from the avdevice implementation) to the hls muxer, and use
>> that instead of using system time (av_gettime()).
>> 
>> I cant use PTS, so what is the correct way to pass "wall clock time"
>> metadata for every frame to the HLS encoder?
>> 
>> I noticed that the decklink implementation uses
>> `av_packet_add_side_data(&pkt, AV_PKT_DATA_STRINGS_METADATA, ...)` to add
>> timecode information, is this the correct approach?
>> 
>
> AV_PKT_DATA_PRFT side data might be the right tool for you.

+1, this seems like the right thing. PTS is not really suitable, as that 
is based (or at least should be based) on monotonic clock, not realtime 
clock.

Probably an AVFormatContext flag should be added, similarly how it is done 
for avcodec.

Regards,
Marton

>
>> I hope this mailing list is appropriate for my question, otherwise please
>> forgive me.
>
> It is only appropriate for this mailing list if you want to improve
> FFmpeg itself (i.e. by making the hls muxer use AV_PKT_DATA_PRFT; the
> dash muxer already seems to use it). If not, the user mailing list is
> the right place.
>
> - Andreas
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