[mythtv-users] MP4/H264 file and problems with 10-second rewind

[Joey Morris]

Joey Morris <rjmorris at nc.rr.com> wrote on Fri, Dec 23, 2011 at 06:02:52PM -0500:
> I bought the Louis CK standup special that he's selling from his
> website and dropped it into MythVideo (0.24.1+fixes). It mostly plays
> fine. However, the elapsed time counter moves at about half of real
> time. For example, if I start the video and let it play for 10
> minutes, the elapsed time shows just 5 minutes. Also, if I use the
> left arrow key to skip back 10 seconds, it actually skips back several
> minutes.
> 
> I'm not sure how to debug this, but I did inspect the file with
> ffmpeg -i. Here is the output:
> 
> Seems stream 0 codec frame rate differs from container frame rate:
>     47952.00 (47952/1) -> 23.98 (2997/125)
> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
>     'Louis CK Live at the Beacon Theater 2011.mp4':
>   Metadata:
>     major_brand     : mp42
>     minor_version   : 1
>     compatible_brands: mp42mp41
>     creation_time   : 2011-12-09 16:04:07
>   Duration: 01:02:43.17, start: 0.000000, bitrate: 2550 kb/s
>     Stream #0:0(eng): Video: h264 (Constrained Baseline) (avc1 / 0x31637661),
>         yuv420p, 1280x720, 2354 kb/s, 23.98 fps, 23.98 tbr, 23976 tbn,
>         47952 tbc
>     Metadata:
>       creation_time   : 2011-12-09 16:04:07
>       handler_name    : Apple Video Media Handler
>     Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, s16,
>         191 kb/s
>     Metadata:
>       creation_time   : 2011-12-09 16:04:07
>       handler_name    : Apple Sound Media Handler
> 
> I suspect this is a frame rate problem similar to the one discussed
> recently in http://www.gossamer-threads.com/lists/mythtv/users/497615.
> A solution was found for that problem, requiring edits to the file's
> metadata, but that was for an mkv.
> 
> Does anyone have advice for how I can fix the frame rate on my mp4
> file? Or, do you think there might be other causes for the problem I'm
> seeing?

After playing around with this for a while, I think I've fixed it.

At first I tried demuxing the mp4 into its separate video and audio
streams, and then remuxing into a container with hopefully the right
frame rate. For demuxing, I tried both ffmpeg and mencoder. For
remuxing, I tried to create an mp4 using both ffmpeg and mencoder, and
I tried to create an mkv using mkvmerge. No matter what I tried, my
final file was bad. It either wouldn't play at all or had no video.

Finally, I decided to skip the demuxing step and instead opened the
original mp4 in mkvmerge's GUI. I left all the settings at their
defaults, including FPS, which was blank. So far, I haven't seen any
problems when playing the resulting mkv in MythVideo. The elapsed time
counter advances at the correct rate, and skipping around in the file
works fine.