Ticket #130 (closed task: fixed)
Audio/Video Sync Problems With Auto-Transcoding
| Reported by: | anna | Owned by: | anna |
|---|---|---|---|
| Priority: | blocker | Milestone: | 4.1 |
| Component: | Transcoding | Severity: | |
| Keywords: | Cc: | ||
| Who will test this: |
Description
Some file formats (particularly wmv and avi) are not being handled well by Indytube/mencoder. The audio is out of sync and the video often appears in fast motion resulting in a 5 minute video lasting only 10 seconds. The audio will continue playing after this. The duration is often reported incorrectly.
Other videos will play more or less normally but the audio will be significantly out of sync.
Here is a version on plumi demo - http://demo.plumi.org/Members/qwerty/videos/cliplarage-medium.wmv/view
And on EM stable http://www.engagemedia.org/Members/AnarchiaFilms/videos/shv-train-track-court-1.mp4/view http://www.engagemedia.org/Members/jonair/videos/nonregularworkersstruggleinnewcoreeland.wmv/view
It seems mencoder has difficulty transcoding files with a variable frame rate. WMV files frequently have a variable frame rate. This may not be the only explanation, but it appears to be the major one.
Attachments
Change History
comment:2 Changed 5 years ago by anna
So what to do here? Seems to me there are at least two possible solutions:
- employ ffmpeg instead of mencoder as from what i have read it is better able to handle A/V sync and variable frame rate input. from andycat's test above this seems to be a good route to take.
- use "harddup" duplicate frames in mencoder, and also look at the potential for determining the average frame rate (which seems to involve asking mplayer to play the file through at a faster speed and report duration and number of frames, getting a script to determine the average) and passing this back to mencoder so it can create the correct number of frames and maintain sync.
we could ask the script to only go through the process of determining an average frame rate IF the frame rate is >15 or >30 - otherwise pass through the frame rate from the metadata. (apparently mencoder reports the frame rate as 1000 if it is variable)
my research notes are here: http://www.plumi.org/wiki/TranscodingErrors
comment:3 Changed 5 years ago by and
- Priority changed from critical to blocker
Anna and I chatted about this yesterday and though we should bump it up to blocker as EM has been getting a few vids in lately that have had this problem. I realise people know this already but just keeping it at the front of our collective minds.
comment:6 Changed 5 years ago by anna
nearly ready to tick this off.. just maybe should re-transcode the EM catalog in order to fully test a variety of formats.
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PREVIOUS COMMENTS AS TICKET HAS BEEN MOVED OVER FROM ENGAGEMEDIA.ORG TRACKER:
10/09/07 03:19:01 changed by anna
APEC: 330 Million Dollar Wall of Shame didn't work: Chasers Comedians
http://www.engagemedia.org/Members/thesaint/videos/apec-snipers.wmv/view
http://www.engagemedia.org/author/thesaint
Errors
sound is terrible - very compressed. picture is not synced - rushes past while audio is at normal speed. black frames remainder of video duration is displayed as 00.02, the video plays out to 01.30, but is listed as duration
Half-widows of Kashmir
http://www.engagemedia.org/Members/Halfwidows/videos/parveena-subtitiling-and-operation-snatch.mov/reTranscode
http://www.engagemedia.org/author/Halfwidows
Errors
video ends abruptly after 58seconds
I have changed indytube.conf back to vbitrate=150 instead of 200
I have clicked restart on these videos: http://www.engagemedia.org/Members/thesaint/videos/apec-snipers.wmv/reTranscode http://www.engagemedia.org/Members/Halfwidows/videos/parveena-subtitiling-and-operation-snatch.mov/reTranscode
Will check these tomorrow, document effect of change (if any) and do the same with the others in review queue also.
10/09/07 03:20:19 changed by anna
Note - i killed indytube processes and restarted all instances, otherwise changes to indytube.conf would have had no effect.
10/10/07 02:07:26 changed by anna
APEC: 330 Million Dollar Wall of Shame didn't work: Chasers Comedians
http://www.engagemedia.org/Members/thesaint/videos/apec-snipers.wmv/view
http://www.engagemedia.org/author/thesaint
Errors
sound is terrible - very compressed. picture is not synced - rushes past while audio is at normal speed. black frames remainder of video duration is displayed as 00.02, the video plays out to 01.30, but is listed as duration
Change After Reverting to Old Bitrate
No change. Same error.
10/13/07 16:19:16 changed by andycat
I used ffmpeg on the cmd line , to make the flv here http://testing.engagemedia.org/Members/jonair/videos/nonregularworkersstruggleinnewcoreeland.wmv/view
I think that works ?
I got some feedback from a guy in FOE Amsterdam, who is using indytube, that they have had the same problems as us. He claimed it was a debian issue, with some code missing from the original mplayer sources. I have got a mplater svn checkout built on the server, but so far its not working.
He also said that they use ffmpeg instead of mencoder, as it is more robust. Hence i then explored that, and here is a flv produced using:
ffmpeg -i /opt/instances/zope-testing/var/files/Members/jonair/videos/nonregularworkersstruggleinnewcoreeland.wmv -ab 56 -ar 22050 -b 500 -s 320x240 nonregularworkersstruggleinnewcoreeland.flv
10/14/07 03:32:38 changed by and
That's interesting. Is it possible to transcode the videos in stable by hand that are currently in the review list? A few have been there for more than a month and given how little content we are getting atm it'd be great to add these 5 videos.
Cool that foe are using it. Are they using plumi also? Be great to encourage him to jump on the indytube list so we could stay in the loop. http://lists.codecoop.org/mailman/listinfo/indytube-coders
10/14/07 03:57:13 changed by and
Also this video, which we _assumed_ :) was cut short in transcoding, is actually only 58 seconds long. http://www.engagemedia.org/Members/Halfwidows/videos/parveena-subtitiling-and-operation-snatch.mov/view I will write to them and tell them to upload the full version.
10/21/07 18:40:24 changed by andycat
I have confirmed on my computer that using the latest SVN version of mencoder, and adding -ofps 20 produces a FLV that has the correct video playback speed - although I think there are video/audio sync issues.
related: http://lists.mplayerhq.hu/pipermail/mencoder-users/2007-October/007316.html
10/21/07 19:45:50 changed by andycat
And , in fact , as that post in the url above mentions, the WMV of jonair's video reports FPS of 1000
but i also dont know the implications of hard copying the "-ofps 20" into the mencoder options in indytube - I dont know if the framerate is passed thru , so to speak, from the input video into the FLV.. ?
I believe it is - I ran
root@redfern:/var/www/stable-flv-files# find . -name "*.flv" -exec flvtool2 -P {} \; -print > res
which is the output of the fvltool2 s info about a FLV eg
/var/www/stable-flv-files/Brendan/videos/g20_summit.flv:
So doing a search of that file..
root@redfern:/var/www/stable-flv-files# grep framerate res
To solve this, we probably need to be smarter about encoding the framerate from the input file.
10/21/07 19:47:33 changed by andycat
http://lists.mplayerhq.hu/pipermail/mencoder-users/2007-October/007348.html
is a thread to watch
10/21/07 20:14:43 changed by andycat
Aah .. http://lists.mplayerhq.hu/pipermail/mencoder-users/2007-March/005534.html 10/21/07 20:18:24 changed by andycat ¶
This is the question we also need answering: http://lists.mplayerhq.hu/pipermail/mencoder-users/2006-October/004364.html 10/22/07 09:13:41 changed by andycat ¶
Links for future reference: converting videos for iPod video using ffmpeg - http://www.julien-oster.de/crash/122.html
http://www.avidemux.org/admForum/viewtopic.php?pid=21862#p21862
http://handbrake.m0k.org/trac/wiki/x264Options
14.7. Using MEncoder to create QuickTime??-compatible files - http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-quicktime-7.html
10/24/07 10:39:54 changed by andycat
Ive added -ofps 30 to indytube.conf on testing
Please test it out on testing.engagemedia.org by retranscoding files, and comparsing them to ones on EM live, esp. the WMVs
10/24/07 11:14:34 changed by andycat
http://testing.engagemedia.org/Members/jonair/videos/nonregularworkersstruggleinnewcoreeland.wmv/view
seems to work on re-transcoding..
To compare between a file that was already working:: http://testing.engagemedia.org/Members/undergrowth/videos/the_black_gst.mov/view http://www.engagemedia.org/Members/undergrowth/videos/the_black_gst.mov/view
Which is think indicates it doesnt work properly. The time on the original track is 12:40 ( user reported - Duration: 12 minutes 41 seconds ) The time on the testing version is 10:33 ( flashplayer)
The metadata is :
/var/www/testing-flv-files/undergrowth/videos/the_black_gst.flv:
From the stable version :
/var/www/stable-flv-files/undergrowth/videos/the_black_gst.flv:
i just dont know exactly what happens when it transcodes from , say, 24 fps, mpeg or whatever to 30fps FLV
Clearly i think we need to match the FPS to the input. unless its whack like WMV.
10/24/07 11:32:06 changed by andycat
So i remembered about 'harddup' which seems to not drop duplicate frames, and keeps audio and video in sync - from my limited understanding of the situation - and added it into testing's indytube.conf
from "man mencoder"
This has keep the correct video length of the transcoded file http://testing.engagemedia.org/Members/undergrowth/videos/the_black_gst.mov/view
The new metadata is :
/var/www/testing-flv-files/undergrowth/videos/the_black_gst.flv:
So now the video and audo play in sync up to the end! The filesize is SMALLER though - which i find weird, since the video is meant to have more frames in the same length of time.. ?
10/24/07 21:51:35 changed by anna
perhaps when it says "duplicating frames" it merely means in the sense that most lossy compressors do i.e. it has one keyframe, then says repeat that frame for each "duplicate" to maintain sync.
could this explain the smaller file size?
also did you consider the question i raised earlier of whether or not we could preserve native framerates unless they fell below 15 or above 30? is this possible?
10/24/07 21:56:06 changed by anna
also if we are going to force a framerate i would suggest 25 for the engagemedia.org site rather than 30 as 25 is the native PAL framerate which people should be uploading more often.
10/26/07 09:04:23 changed by andycat
From http://gentoo-wiki.com/TIP_MEncoder_Tips_and_Tricks
To encode the movie with the NTSC framerate of 29.97 frames per second:
NOTE: 29.97 is an approximation, more accurately, it's 30/1.001 (same applies to 23.976, it's more accurately 24/1.001). New versions of mencoder support fractional values, and thus can be used here
mencoder <filename.avi> -ovc lavc -oac mp3lame -o <output.avi> -ofps 30000/1001
To encode the movie with the PAL framerate of 25 frames per second:
mencoder <filename.avi> -ovc lavc -oac mp3lame -o <output.avi> -ofps 25
Note that you will have A-V sync problems if the framerate of the source does not match the output. See the docs for information about using telecine in these cases.
Telecine is http://en.wikipedia.org/wiki/Telecine
and then somebody needs to digest this i reckon http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-telecine.html :)
11/28/07 00:17:04 changed by anna moving to Plumi tracker.