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Compressor: H.264 data rate difference between local and distributed encode

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Matt Riley
Compressor: H.264 data rate difference between local and distributed encode
on Nov 6, 2009 at 9:21:54 pm

Doing some testing today and noticed this curious behavior with Apple Compressor 3.5.1:

Set video encode for a 50 second 1080i uncompressed file to H.264 at 50000 kbps (50 mbps). Audio is 24 bit, 48khz stereo with no compression.

1. Sending the job to "This computer" for a local-only encode gives me a file size of 327 MB
2. Sending the same job to the same computer using distributed encoding gives me a file size of 211 MB

The data rate for the distributed encoded file is about 34 mbps, which isn't what was specified in the encode settings in Compressor. The data rate for the locally encoded file is about 52 mbps, which is what I would expect when the audio is taken into account.

Why the difference? Both encoded files are the same duration, so there aren't any missing frames. They both look good and play well but this is giving me cause for pause.

Also, another curious difference I noticed... The distributed file has the More Info fields populated with useful information in the Finder (dimensions, codecs, duration, channel count, total bit rate). The locally encoded file does not have this information. Weird.

-Matt

PS--This testing is being done to meet some DG Fastchannel specs that were sent to me.


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