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recompress H264 with video pass-through

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Steenebruggen Mathieu
recompress H264 with video pass-through
on Sep 2, 2009 at 11:00:29 am

Dear all,

As you probably guess, I have a big problem with compressions...

I explain: we received a job from a client to digitalise a whole batch of tapes footage (Beta SP, Digibeta, Beta SX, etc.) in flash format. We are working here with Final cut studio 6 (therefore, compressor for compressions).

So, we captured the whole batch, and then, sent it to Compressor to make a quick time compression in H264 codec, with the f4v extension, to make video files readable by flash player. It took a lot of time, but everything went great. The client (not a technician) received the hard drive with more or less 500 files and told us that it was all good...

But... one week later, one of his technician told us that he had a problem with the sound codec used in this first compressions (Little endian, 16 bit 48000 hertz) and that he would like AAC sound 41000 hertz.

The major problem is that meanwhile, we erased all the capture scratch, so we only have the f4v files (with the false audio codec) left...

I tried to recompress one of these files once more, using the same codec for video (QT H264 .f4v) but with AAC codec for the sound. The problem is that when I do that, the recompressed file looks like it is playing at 15 fps, instead of the 25 fps used in the compression. Just to answer the question you maybe ask : the information of the file when I read it well indicates a 25 fps file.

I guess this comes from the fact that I recompress a QT h264 file into another QT h264 file.

So my question is : does anybody have any idea how I could make a kind of compression with a video pass-through option, to only recompress the sound, and not the image?

Or if you have any other idea which could avoid me to have to re-capture the whole batch, it would be more than welcome!

Thanks in advance for your help!

Mathieu.




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Brian Alexander
Re: recompress H264 with video pass-through
on Sep 2, 2009 at 9:32:49 pm

I don't think there's an easy answer because of the sheer volume you have to work with. The only way I can think of is going to require each one to be done by hand.

I would create a custom setting for this job, disabling video and just compressing the audio. You'll end up w/500 audio files which you can simply "add to movie" in QuickTime and delete the little endian audio track.

Brutal, but that's all I've got.

Good luck.

--
Brian Alexander
Sr Video Engineer
Freeman AVS


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Steenebruggen Mathieu
Re: recompress H264 with video pass-through
on Sep 3, 2009 at 10:22:47 am

Dear Brian,

Thank you very much for your suggestion. This was indeed a good idea, I made one try as you suggest, but unfortunately, I doesn't work quite well :
-I can indeed, on the G5 used to make the compression, change the audio track, add the 'good' AAC sound, and erase the 'bad' little endian. when I play it on the same machine, it works fine, I read the file correctly with the good sound codec.

But... when I save the new QT file, and take it on another computer, the sound disapears. From what I understand, it is because Quick time only makes a link to the AAC sound file, and when I save it, it doesn't create an embedded file (by the way, after saving, the file size stays the same than the original file size with little endian sound), so when I play it on another computer, there is simply no more sound... (but I guess the little endian sound is still there, as the size of the file didn't change).

So, the only way I know to create an embedded file in QT, is to export it, but when I do that in QT, I get the same image problem (seems to be playing at 15 fps) than when I was doing that with compressor... I understand the feeling of the Snake bitting its own tail ;-)

I don't know if you have any other suggestion to create the QT file besides making an export, it would be welcome if you do!

PS : even wearder : when I try the same compression in compressor with an older G5 (which has the same softwares, and same versions), the new H264 files plays well and doesn't have this problem of images playing at 15 fps...

Instead of being lost in translation, i get lost in compression... ;-)

Thanks again for your help!

Mathieu.



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Daniel Low
Re: recompress H264 with video pass-through
on Sep 3, 2009 at 8:54:42 pm

http://forums.creativecow.net/readpost/20/863329



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"There's no chance that the iPhone is going to get any significant market share. No chance."

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Daniel Low
Re: recompress H264 with video pass-through
on Sep 2, 2009 at 9:44:32 pm

I think Episode (from Telestream) can do this....Craig?

__________________________________________________________________
"There's no chance that the iPhone is going to get any significant market share. No chance."

Steve Ballmer To USA Today


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Craig Seeman
Re: recompress H264 with video pass-through
on Sep 3, 2009 at 9:09:20 pm

Yes, Telestream Episode has a pass through feature for either video or audio. I've seen a case or two where the file size inexplicably increased significantly so I'd test with one file first.



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Steenebruggen Mathieu
Re: recompress H264 with video pass-through
on Sep 4, 2009 at 3:07:38 pm

Thank you all for your help and answers!

After quite some digging, tests, and unsuccesful attempts of all kind, I figured out a way to do the trick!

I explain it here under, in case someone faces the same kind of issue : (I know it is tricky, but it works, and all automated!)
-In fact, I finally used QTpro to do the conversion. I made an export setup as follows :
export movie to MP4, then, in the settings of the video, it is possible there to make a 'video pass thru', and I just changed the audio codec in the one I needed : AAC 44,100 htz. The compression is of course reallly quick, because it only compress the sound. And the video stays absolutely the same as the original - no more problems of video playing at 15 fps.
-Then, to be able to make the 500 files not one by one, I used Automator (thanks Apple ;-) with an Action that I found on the web which is : 'Export in QT with the most recent settings'. I can so do a batch of a large number of video file (I don't do them all at once, because the files then stays open in Quick time, and if I made the 500 files all at one, I am afraid the computer could crash) I send them 50 by 50 , which already saves a lot of time!
-After that, I find myself with all my video files with .MP4 extension (but I need them with .f4v extension), and just use 'name mangler' to change the extension all at once.

And that's it!

Hope this can help someone else one day!

Mathieu.


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