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K750i 3gp mp4 creation expertise |
leibniz
Joined: Mar 04, 2003
Posts: 102
From: Western Canada
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I know there's a big thread on K750i/W800 video discussion, but I'd like to get real specific here for a moment...
Anyone using linux command line and ffmpeg to create 3gp and mp4 files?
I have this process working, but I would like to find that perfect middle ground between size, and quality. Personally I've found 8000 sampling rate too low (too much hiss) but 24000 sounds good.
I'm using the following ffmpeg parameters:
-f mp4 -avcodec mpeg4 -r 16.5 -s qcif
It's all pretty standard (for SE K750i resolution), About the only place to gain any space I think, is by altering the sound quality.
I've been trying with aac and ac3.
Downsampleing audio using -acodec aac -ab 32 -ar 24000 saved alot of space, and imho, the quality is very acceptable.
Here are some tests I've done with varying audio quality on a 1 minute sample:
Output #0, mp4, to 'yr8.mp4':
Stream #0.0: Video: mpeg4, 176x144, 16.50 fps, q=2-31, 200 kb/s
Stream #0.1: Audio: aac, 48000 Hz, stereo, 64 kb/s
= 2407456 2006-03-06 09:17 yr8.mp4
Output #0, mp4, to 'yr6.mp4':
Stream #0.0: Video: mpeg4, 176x144, 16.50 fps, q=2-31, 200 kb/s
Stream #0.1: Audio: aac, 24000 Hz, stereo, 32 kb/s
= 1916637 2006-03-06 09:18 yr6.mp4
That's about a 20% savings in file size. That adds up on big files (1/2 hour shows or longer.)
3gp files using the same audio parameters were slightly larger (1%) so it looks like mp4 is the way to go.
Using ac3 audio with downsampling audio saved even a little more:
Output #0, mp4, to 'yr4.mp4':
Stream #0.0: Video: mpeg4, 176x144, 16.50 fps, q=2-31, 200 kb/s
Stream #0.1: Audio: ac3, 24000 Hz, stereo, 32 kb/s
= 1667437 2006-03-06 09:26 yr4.mp4
That's another 14% saving on size. The problem I have with this is that I get no sound using the ac3 filter. Not sure if it's my ffmpeg setup or something else.
Anyway, has anyone else played with audio filters? I'd like to use the most efficient one to save as much space as possible, while retaining as much quality as possible.
Using the above examples, it's just under 2 MB per minute of mp4 file. That's about 53 MB per 1/2 hour show. Perhaps thats normal, I don't know.
Please post your observations.
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leibniz
Joined: Mar 04, 2003
Posts: 102
From: Western Canada
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T'aint nobody usin' linux and ffmpeg to create 3gps and mp4s??
Ok. I guess I can believe that.
I was looking to get every ounce of efficiency in the conversion stage, but I guess I can live with 2MB / minute of mp4 video with acceptable audio.
I'll just have to buy a few 2GB cards if I want to put all my favorite episodes on there, that's all. | |
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Posted: 2006-03-06 16:45
