[FFmpeg-devel] Using copyts with mpegts output fails after 26, 5 hours

[Devin Heitmueller]

Hello Panagiotis,

> On May 3, 2019, at 4:50 AM, Panagiotis Malakoudis <malakudi at gmail.com> wrote:
> 
> As I mentioned in ticket http://trac.ffmpeg.org/ticket/7876 this is
> not my code, I just adapted it for current git. It is also very old
> code (back from 2012), probably it fitted OK back then. This code
> fixes this specific issue reported in the ticket. If it breaks other
> things, then of course it can't be commited. Still there is a need for
> a fix for the reported issue in the ticket, as it is you can't
> transcode with -copyts above 26,5 hours, it fails after that.
> 

For what it’s worth, this is a pretty difficult problem, and not one exclusive to -copyts.  I had to put a bunch of code in the demux to support the TS wraparound for use with the decklink output, which supports a 90KHz clock but the value is 64-bits, so the output doesn’t expect it to jump back to zero after hitting the 33-bit limit.

Also, at least in my case, the existing wraparound code that was there works exactly once - even in cases where it worked as expected it would properly handle the wraparound after 26.5 hours, but then fail after 53 hours.

The approach I took was to track the PTS values as they approached 2^33, and then have a separate wraparound count such that the values coming out of the demux keep incrementing past the 33-bit limit.  This works well for the TS output case as well, since the output will simply truncate the lower 33-bits and it will continue working as it was before.  But, as Michael suggested, it almost certainly breaks seeking.  While my use cases don’t rely on seeking since I’m doing 24x7 decoding of realtime TS streams, such prevents my patches from being accepted upstream as well.

I’ve got no easy answers to this one - having TS streams longer than 26.5 hours and expecting seeking to work properly seem like they are not compatible concepts.

Devin

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Devin Heitmueller - LTN Global Communications
dheitmueller at ltnglobal.com