Video from Plextor ConvertX cannot be transcoded

[mythtv@…]

I recently installed a Plextor ConvertX external tuner with MPEG4 hardware encoding. It works wonderfully, except when I try to transcode the video to remove commercials (I use lossless transcoding), the resulting video is completely garbled.

If it would help, I can provide a clip recorded with the ConvertX to be used for debugging.

-Austin

[mythtv@…]

A new note: I have found that sometimes, if don't encode video anywhere near the beginning or the end of a show, the video turns out alright, but this is not consistent.

More surprisingly, at one point I was able to go through the episode a little bit at a time in edit mode, it found a frame (or keyframe) that appeared normal. Then I backed up through the episode, and the entire episode was viewable as normal. This makes me think the shows are being formatted incorrectly, and are completely intact if the problem could be resolved.

I wish I knew more about the MPEG4 format, I'd see if I could find the problem myself.

[anonymous]

I have the same problem and have noticed that it's intermittent also. I only transcoded one video when I was running 0.19 and it was successful, but ever since I upgraded to 0.20 I was only successful on the first 2. I have also noticed something odd. It appears that when I try to use mythfrontend on the television (svideo output) it is garbled. However, if I share the files using samba and play them back on my PC, they appear to work. I have divx installed on my pc - I'm wondering if the divx decoder/encoder isn't working correctly on the frontend - similar to what you're suggesting about finding a keyframe? I'm using mplayer and have recently upgraded to 0.20.

AMD x64, 1GB ram, 0.20, nvidia fx5200, montego ddl sound card

[dale]

Another recent observation. I actually have two ConvertX tuners. The other day I was playing with LiveTV and PiP and when I swapped the PiP and the main frame, the same kind of distortion showed up on the main frame. So I don't think this issue is limited to transcode, it's possibly more of a general "syncing" issue in playback of Plextor video? Just a thought.

[anonymous]

I wonder if the changes made to get seeking working better need to be applied in transcoding as well?

​http://www.mail-archive.com/mythtv-commits@mythtv.org/msg05396.html

Maybe transcoding needs to respect the keyframes written into the container? Or maybe there is a bug where these are being written into the container? This bug makes transcoding with a convertx tuner useless, it's fairly painful.

[Dale]

I have finally found one way of editing video captured by my ConvertX tuners via mythtv.

I installed "avidemux". It can read the .nuv files fine. I was able to edit the video, and through the process of elimination, discovered these settings work for me: video: xvid4

configure: pixel aspect ratio: 4:3

audio: copy format: avi shift: -1200

You'll probably have to play with the "shift" setting to get the audio and video synced correctly.

One other interesting note, with video set to "copy" the resulting video has the exact same problems as lossless transcoding in mythtv does. I'm not sure what that means. One thing that occurs to me is that transcode to mpeg4 might work for convertx users in mythtv too. I'll give it a shot sometime.

[mythtv@…]

Interesting. I've been toying with this off and on since I submitted the bug 9 months ago, and I have a few ideas as to where the problems may be. I think I'm going to try and write a command line script that will repackage the video and fix any errors that may exist. Then I can use that as a job and run it immediately after a job finishes recording. Then maybe we'll be able to transcode the video and remove commercials. I imagine the fixes could be implemented in mythtranscode, but I'm not going to touch it for fear of breaking the transcoding of "normal" video.

[mythtv@…]

It appears that nuvexport is also able to export, at least to Xvid (I haven't tried anything else yet), plus it applies the cutlist as it transcodes. Assuming I can transcode to DVD (my next test), it will let me get the movies I've recorded off my box, and resolve my primary concerns.

I still hope somebody can work this out, but it's looking a bit better than it was.

[anonymous]

Replying to mythtv@ausiv.com:

It appears that nuvexport is also able to export, at least to Xvid (I haven't tried anything else yet), plus it applies the cutlist as it transcodes.

Yes, if you force it to reencode the video to Xvid (say by making the recording size and transcoded size slightly different) then it actually works.

[robertm]

Closing as ancient and invalid. The only codec which can be losslessly transcoded is MPEG-2 video.

[cpinkham]

If this still happens with current trunk (or 0.22 when it is released), please provide a sample recording and I may be able to take a look, otherwise we'll leave this closed. I don't even use my Plextor anymore, it's been buried in a box somewhere for at least 18 months.

[anonymous]

Replying to robertm:

Closing as ancient and invalid. The only codec which can be losslessly transcoded is MPEG-2 video.

This may be ancient, but it's still a problem. Anything recorded with a Plextor ConvertX is completely unviewable after being transcoded -- I'm not talking about a few extra artifacts. I'm not suggesting we should be able to transcode them losslessly, but they should be viewable after transcoding.

I don't particularly care if this gets fixed, as I'd probably keep using the nuvexport workaround for the sake of having a more portable AVI file, but I don't think robertm understands the problem in marking it invalid.