ffmpeg2theora

Chipmunk Audio on select sources

Bug #671703 reported by Andrew Chiw
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ffmpeg2theora
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Bug Description

I'm using ffmpeg2theora 0.27 on Windows with Avisynth to encode video for a streaming site. Once in a while, I've noticed that when I play the resulting .ogv files back with Media Player Classic Home Cinema 1.4.2499.0, I hear the audio sped up 2x at least. In Firefox 3.5, only the video plays - the audio track doesn't.

The Avisynth file I'm using for input is the same for the sources that don't have this chipmunk problem.
DirectShowSource("path",fps=23.976, audio=true, convertfps=true)
LanczosResize(848,480) # Lanczos (Sharp)
TextSub("something")
and maybe ConvertToYV12() depending on whether I used MeGUI on that .avs file before or not.

One thing I've noticed is that in such cases ffmpeg2theora always detects 6 audio channels from the .avs file, when the source only has 2 channels. Maybe that's why? I tried adding -c2 to the command line, but it didn't help. In any case, it detects 2 channels sometimes, and those seem to work fine. I'll check more of my encodes and see. I must use the .avs file to burn subtitles into the video.
I think it only happens with AAC-LC stereo 48kHz/44kHz sources. The videos with MP3 audio encode just fine.

Said video can be found here under the Flash version - if you download it you will find that the audio plays in MPC-HC but is sped up; and it has 6 channels according to MediaInfo.
http://shitteru2.net/anime/kami-nomi-zo-shiru-sekai-episode-1/

I also reencoded an excerpt from a different series, specifically [gg] Soredemo Machi wa Mawatteiru - 01v2 [714A9D82].mkv, which you can find online everywhere:
http://www.mediafire.com/?q14mddbl47pil37

Is there another Theora encoder that isn't as buggy? I'm rather disappointed with the current state of encoders available for Theora. ffmpeg2theora works most of the time, but I wish it would work all the time.

See original description
Revision history for this message
Andrew Chiw (randomshinichi4869) wrote :

I think it only happens with AAC-LC stereo 48kHz/44kHz sources. The videos with MP3 audio encode just fine.

description: updated
Revision history for this message
ogg.k (ogg-k-ogg-k) wrote :

Hi. As an aside, may I point you to https://bugs.launchpad.net/ffmpeg2theora/+bug/660122 in case you've not seen my comment there about a month ago, as I'd like to fix the bug you found, if there is one. Thanks.

Revision history for this message
ogg.k (ogg-k-ogg-k) wrote :

Oddly, I downloaded the start of the MP4 file (kaminomi-01.mp4), and encoded with:

./ffmpeg2theora -x 320 -y 200 -o FOO-kaminomi ../kaminomi-01.mp4

The resulting ogg file plays fine, and audio seems correct, and in sync with the video.
It has two channels:

$ oggz info FOO-kaminomi
Content-Duration: 00:00:12.137

Skeleton: serialno 0925981002
        6 packets in 5 pages, 1.2 packets/page, 2.139% Ogg overhead
        Presentation-Time: 0.000
        Basetime: 0.000

Theora: serialno 0925981000
        295 packets in 99 pages, 3.0 packets/page, 1.071% Ogg overhead
        Theora-Version: 3.2.1
        Video-Framerate: 23.976 fps
        Video-Width: 320
        Video-Height: 200

Vorbis: serialno 0925980999
        649 packets in 28 pages, 23.2 packets/page, 1.278% Ogg overhead
        Audio-Samplerate: 48000 Hz
        Audio-Channels: 2

Might be a difference in the ffmpeg versions used. I'm using:
ffmpeg2theora 0.27 - Xiph.Org libtheora 1.1+ 20100314 (Ptalarbvorm)
compiled with a ffmpeg from late march.

Revision history for this message
Andrew Chiw (randomshinichi4869) wrote :

No, only happens when you open a source video with AAC audio through an AVS file. Directly opening the source file won't induce the bug.

When you do so, ffmpeg2theora should report 6 channels instead of 2, and the resulting video will have chipmunk audio played through MPC-HC, and no audio at all when played in Firefox.

And I must use AVS, I want to hardsub the subtitles.

Revision history for this message
Andrew Chiw (randomshinichi4869) wrote :

And I don't think it's Avisynth: because source videos with MP3 audio tracks work just fine.

Revision history for this message
Andrew Chiw (randomshinichi4869) wrote :

This is what I'm talking about:
http://shitteru2.net/wp-content/uploads/videos/anime/Kami%20Nomi%20zo%20Shiru%20Sekai/kaminomi-01.ogv

Revision history for this message
ogg.k (ogg-k-ogg-k) wrote :

If you run 'ffmpeg -i file.avs', file.avs being the file you give to ffmpeg2theora, ffmpeg should print basic information about that file, including number of audio channels. Does it see 6 channels ? If so, then this seems to be a problem with either ffmpeg or the avs file.

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