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I'm taking responsibility for maintaining a collection of recordings from online meetings, and I'm at a loss to determine which encodings I should use for them. The videos are coming from GoToMeeting, so they emerge in g2m4 format (which is quite large on disk) and so first I transcode with g2mtranscoder from Citrix. This gets me partway there, since other transcoders can work with my files once they're in normal wmv format.

However, from there--what is a proper choice of audio/video codecs? My main goal is to minimize storage, and I'm willing to accept some artifacts from lossy codecs.

My first attempts were using VBR h264 and 32kb/s MP3 in an MP4 container, and this worked well to minimize storage. However, I found that these transcodings could not be indexed when played in VLC: clicking most the way through a 2h video, the audio indexed to the correct time, but the video just froze.

This happened with two separate videos so I thought maybe it was my choice in codecs or something. Is there a better choice?

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Yep! that's right. g2m4-wmv, then wmv-mp4. –  bwerks Jan 5 '13 at 16:58
    
Probably does--I was using VLC to do the second transcode, but it doesn't appear to support keyframes in the UI and the command line documentation is illegible. I'm going to try to FFmpeg, I think. –  bwerks Jan 5 '13 at 17:03
    
From my experience there's usually no problem seeking through H.264/MP4 files generated by FFmpeg. Try something like the following: ffmpeg -i in.wmv -c:v libx264 -crf 25 -c:a libfaac -q:a 50 out.mp4 for a low quality approach. Decrease the CRF (it's like VBR) and increase the Q for better video/audio quality respectively. Default CRF is 23, and lower than 18 would be unnecessary. Default Q for FAAC is 100%, I chose 50% since 32kB/s MP3 seemed enough for you. –  slhck Jan 5 '13 at 17:07
    
The FFmpeg build from 2013-01-04 doesn't recognize libfaac as an encoder. This is a difficulty I've faced both with VLC and with FFmpeg--how can I enumerate supported codecs? –  bwerks Jan 5 '13 at 17:23
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FFmpeg's native AAC encoder (-c:a aac) does not perform VBR encoding for AAC. FAAC can, but that's going to be hard to accomplish with Windows without an FFmpeg version that bundles it. –  slhck Jan 5 '13 at 19:56

1 Answer 1

Your choice is correct. H.264 video + MP3 audio in MP4 is supported by almost all the devices and PCs.

Regarding the seek options (indexing) you should put key frames at regular intervals. Generally speaking, one should have a key frame every three seconds. Most transcoders have keyframe, I-frame or IDR (Instantaneous Decoder Refresh) options where you can set this. Another possibility would be to set the GOP length, which also defines the keyframe interval.

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