[FFmpeg-trac] #8844(avformat:open): DVB subtitles don't work without PCR any more

FFmpeg trac at avcodec.org
Thu Aug 13 00:53:30 EEST 2020

#8844: DVB subtitles don't work without PCR any more
             Reporter:  mkver        |                    Owner:
                 Type:  defect       |                   Status:  open
             Priority:  important    |                Component:  avformat
              Version:  git-master   |               Resolution:
             Keywords:  mpegts       |               Blocked By:
  regression                         |
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  1            |

Comment (by JEEB):

 I have no real preference on this. Personally, I have mostly seen such
 blind mux of TS packets with DVB teletext, and not with DVB subtitles
 (although thankfully this is not too popular - just something you end up
 seeing every now and then).

 And yes, the re-timing logic already existed and since both formats were
 within that if both are affected. The reasoning to add the NOPTS logic was
 to not make it so that if you first get a subtitle packet, and *then* PCR
 is received, you would not suddenly have a f.ex. 8 hour time difference
 between these two packets in your API client, leading to quite hilarious
 results. On the other hand, NOPTS makes no promises about what the
 timestamp is, and API clients seem to handle it OK (including ffmpeg.c)

 That said, for the DVB subtitle parser clearly NOPTS is a special value,
 and the unsetting of timestamps shouldn't be applied to it. That can
 either be handled by removing DVB subtitles from the re-timing logic
 (which apparently was required for some sample looking at the commit
 message?), or at least excluded from the NOPTS logic.

 I will for now post a patch doing the latter, and which way forward is
 better can also be discussed in that thread.

 Normal streams without the PCR removed are unlikely to have been affected
 largely since as soon as you received PCR, the possibility of the
 timestamps being NOPTS'ified would get removed.

Ticket URL: <https://trac.ffmpeg.org/ticket/8844#comment:4>
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