Trimming/Reencoding DTT recordings with FFMPEG?

liamf

Hi,

I have a mythtv setup and can record DVB-S (freesat) or SaorView (DVB-T)

I have been using ffmpeg on Ubuntu to trim recordings I want to keep to the correct length, drop out extra audio channels and so on.

With recordings from DVB-S (SD or HD) this works fine.

With recordings from SaorView, this does not work. I end up with a file of plausible looking size, but which will not play back in VLC or XBMC. The original recording always plays fine.

The ffmpeg command I use is generally:

ffmpeg -i <original recording> -map 0:x -map 0:y -vcodec copy -acodec copy -ss <start> -t <duration> <outputfile>

I have never seen this fail to produce the correct output when trimming DVB-S SD/HD content.

I am pretty sure this never works when trimming DVB-T content: not 100% certain of that, since I just have a unified channel list and tend to forget where I recorded things from. But since I have been paying attention I have never got it to trim SaorView recordings.

I have tried both the ffmpeg and x264 which come with the standard Ubuntu 9.10 install, and throwing those away and building the latest ffmpeg 0.6.1 and x264 from source.

One of two things happens:
- ffmpeg churns through the file, and produces a 0KB output file
or
- ffmpeg churns through the file, and produces a large file of roughly the correct size, which refuses to play (video) in VLC or XBMC

This is annoying as I am one of those people who likes the recording of the movie to start with the studio logo and end with the end credits. And not with 10 minutes of commercials before and after ... :-)

Hints accepted gratefully

Regards
Liam

STB

TS files ?

run it through tsdoctor first. It will filter out the rubbish. Only takes a minute.

liamf

Ah. Good thinking.

The output from ffmpeg, when fed the DTT recording, is not in mpegts format. For some reason. Although the input is.

So explicitly adding -f mpegts to the ffmpeg command line fixes it up nicely and the trimmed recording plays correctly.

Thanks!

watty

I haven't used it in years

http://www.offeryn.de/dv.htm
PVAStrumento

It converts Transport Stream files to Program Stream Files. It should work for MPEG4 video too as it doesn't do anything to the actual video & audio data.

Fixes some kinds of errors and allows splitting/combining/trimming and sync offset change.

liamf

Thanks for the tool reference.

There are so many out there to experiment with ...

ffmpeg though seems to have sufficient options to keep me occupied experimenting with them for ages.

Plus I have some professional mux/demux s/w at work if things get more challenging.

STB

I am surprised that it works straight off. Most of the MPEG4 TS file is full of PAT info that VLC hates.

For DVB though Cypheros TSDoctor is fantastic but not free (the trial is). There is nothing that it cant fix very quickly. Especially when you get into MPEG4 H264 HD files.

I use Avidemux, All to AVi and Xilisoft for my various needs.

liamf

Works fine ... I tested playback with XBMC.

And recording it in myth doesn't give you the full TS of course: you just get a sort-of stripped down single program TS with a single service in it.

Anyway, ffmpeg is my friend again now.