[FFmpeg-devel] Experiences in using ffmpeg to transcode broadcast video

[Mika Raento]

Tickets for sub2video and async not working with non-monotonic input, using
-copyts:

https://trac.ffmpeg.org/ticket/4062
https://trac.ffmpeg.org/ticket/4064

Hm. Lots of my issues seem to relate to using -copyts. I had trouble
keeping all video and all audio if there were periods where one or the
other were missing (esp. in the beginning). Maybe I could make this simpler
if I'd relax that requirement (I don't know how much happier my users are
if they get audio but no video, rather than nothing).

    Mika

On 29 October 2014 10:38, Mika Raento <mikie at iki.fi> wrote:

> segment muxer PIDs were fixed in
> https://github.com/FFmpeg/FFmpeg/commit/502fc3b3d4b36015562d19d74f27d0a4ff835c4e
> by me
>
> On 29 October 2014 10:17, Mika Raento <mikie at iki.fi> wrote:
>
>> Hi
>>
>> Thanks for the feedback.
>>
>> I'll try to capture at least some of these in tickets, and reply on this
>> thread as I go along.
>>
>> Async not working with damaged audio input is
>> https://trac.ffmpeg.org/ticket/2693 (existing ticket)
>>
>> Sub2video not working with negative timestamps is
>> https://trac.ffmpeg.org/ticket/4062 (new ticket)
>>
>>     Mika
>>
>> On 27 October 2014 01:00, Michael Niedermayer <michaelni at gmx.at> wrote:
>>
>>> On Wed, Sep 24, 2014 at 10:43:40AM +0300, Mika Raento wrote:
>>> > Dear all
>>> >
>>> > This mail is meant mainly as a note to other potential users, but
>>> > possibly as input to development - time allowing I might be able to
>>> pick
>>> > up some of the pieces myself. It's also a thank-you for all the hard
>>> > work in ffmpeg.
>>> >
>>> > I've successfully implemented a transcoding pipeline for producing
>>> > multi-bitrate fragmented mp4 files from broadcast DVB input. More
>>> > concretely, I'm taking in broadcast TS captures with either mpeg2 video
>>> > and mp2 audio (SD, varying aspect ratio) or h264 video and aac audio,
>>> > both potentially with dvbsub. From that I'm producing ISMV output with
>>> > multiple bitrate h264 video at fixed 16:9 aspect ratio and multiple
>>> > bitrate aac audio, with burned subtitles. The ISMV outputs are
>>> > post-processed with tools/ismindex and with the hls muxer.
>>> >
>>> > There are number of limitations in ffmpeg that I've had to work around:
>>> >
>>> > - I haven't gotten sub2video or async working without reasonably
>>> >   monotonous DTS. Broadcast TS streams can easily contain backward
>>> jumps
>>> >   in time (e.g., a cheapo source that plays mp4 files and starts each
>>> file
>>> >   at 0). The fix is to cut the TS into pieces at timestamp jump
>>> locations
>>> >   and using '-itsoffset' to rewrite the timestamps and then
>>> concatenate.
>>> >   I'm using the segment and concat muxers for that.
>>> > - Sub2video doesn't work with negative timestamps, so I use
>>> '-itsoffset'
>>> >   to get positive timestamps
>>> > - For HD streams, I need to scale up the sub2video results from SD to
>>> >   HD. Sub2video doesn't handle the HD subtitle geometries. I'm not
>>> >   enough of an expert to know whether that's the issue, or whether
>>> that's
>>> >   just the way it's supposed to work with SD subs (typical) with HD
>>> video.
>>> > - For columnboxing, I use the scale, pad and setdar video filters.
>>> These
>>> >   work fine, but their parameters are only evaluated at start, so I
>>> need
>>> >   to cut the video into pieces with a single aspect ratio first and
>>> >   concatenate later.
>>> > - Audio sync (using aresample) gets confused if the input contains
>>> >   errors, so I need to first re-encode audio (with '-copyts') and only
>>> >   after that synchronize.
>>> > - The TS PIDs are not kept over the segment muxer, so I given them on
>>> >   the command line with '-streamid'.
>>>
>>> a bit late reply but
>>> bug reports or feature requests for all these are welcome unless there
>>> are already tickets for them assuming these issues still exist
>>>
>>> thx
>>>
>>> [...]
>>>
>>> --
>>> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>>>
>>> Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
>>>
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>>>
>>>
>>
>