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Audio woes
I’m lightly editing videos of lectures in a university class: adding a title, deleting long pauses, inserting occasional fades associated with long pauses, and placing chapter markers for navigation.
The camera produced H.264 video with only the left channel of audio stereo, and I use Compressor to produce 422 ProRes with mono audio. After editing in FCP, I export to QuickTime, then process this in Compressor, generating a .mov file with H.264 compression.
Almost every time I export from FCP to QuickTime, one or more extended region of that movie has defective audio, usually but not always starting and stopping on a cut I had made. There are periodic squawks, and repeated overlaying of an audio phrase from somewhere else in the video. It makes no difference whether I export QuickTime self-contained or reference-only. Trying the export again makes no difference. The audio is fine within FCP.
In some cases I’ve been able to get a usable output by strange strategems such as copying the region of the sequence where the output has the bad audio, pasting into a new sequence, dragging to the browser as a new clip, dragging to new channels of the original sequence, and deleting the old portion of the original sequence. This is hit-or-miss and enormously time-consuming. I’m getting scared because I have a very large number of videos to produce. I even tried doing this work in Adobe Premiere on Windows, but there I was dismayed to find that the best compression I could do gave me final videos twice as large as I could make with FCP/Compressor, if and when the latter works.
Environment: I’m working on a MacBook Pro. I’ve tried working with files on the Mac and I’ve also tried working with the files on a large USB drive. The results are exactly the same.
Does any of this sound familiar? Is there something “obvious” that I’m doing wrong, or failing to do? This forum has already helped me as a newbie by telling me to compress to 422 ProRes before attempting to edit, and to export to QuickTime before processing with Compressor. I’m hopeful that someone can tell me how to deal with my extremely serious problem. Thanks.
Bruce Sherwood
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8 Replies
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Try exporting straight to compressor and of course you can preview it while doing that also check your audio settings, 48k is usually the best but 44 might be needed, it depends on what rate the camera took the original footage.
Remember with exporting you want to go through as few compressions as possible.
aka Newbie Wan Kenewbie. “The young Newbie, is now a Padawon.”
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Thanks. The original camera output was H.264, 720×480, Millions, AAC, 2 channels, 32000 Hz. As I mentioned, only the left audio channel actually has data; the right channel is empty.
Thinking to save a step, when I transcoded to 422 ProRes I specified 16000 Hz mono. Given your comment about avoiding all intermediate compressions, maybe that’s where my problem lies.
Bruce Sherwood
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Yup, I’d put a fairly sizeable wager that that’s where you’ve gone wrong, try again without converting to 1600 hz and just leaving as is, when you export, leave the audio as current, or you might have to adjust to 32k but try leaving the audio alone first and see what happens.
aka Newbie Wan Kenewbie. “The young Newbie, is now a Padawon.”
System
Mac Pro 2.8Gb quad core
8Gb RAM
1x 320Gb 7200 hardrive
1x 1Tb 7200 hardrive
Nvidia Geforce 8800 512mb Graphics card
1x 1Tb external WD ‘My Book’ eSataEquipment
Panasonic AG-HVX 200
Firestore FS-100 -
Exporting to Compressor worked, where exporting to Quicktime didn’t.
In the future I’ll be sure when transcoding from the camera video to ProRes to leave the audio alone.
Bruce Sherwood
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When I transcode from the camera video to 422 ProRes, if I leave the Compressor audio setting at pass-through, the audio isn’t rendered (the camera video is stereo AAC 32000 Hz).
What should I specify in Compressor in order to get a 422 ProRes file that is immediately editable in FCP, without further rendering?
Bruce Sherwood
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Try setting the audio to 32khz same as when you shot it.
aka Newbie Wan Kenewbie. “The young Newbie, is now a Padawon.”
System
Mac Pro 2.8Gb quad core
8Gb RAM
1x 320Gb 7200 hardrive
1x 1Tb 7200 hardrive
Nvidia Geforce 8800 512mb Graphics card
1x 1Tb external WD ‘My Book’ eSataEquipment
Panasonic AG-HVX 200
Firestore FS-100 -
When you use Compressor to make the Pro Res file set the Audio settings in the Encoder tab of Compressor’s Inspector to PCM Linear, 48kHz, 16 or 24 bit. That’s what all professional NLEs expect to see. Setting the audio otherwise invites all sorts of not-so-good results, particularly, when encoding your final H.264.
John
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I did try 16 bit 32 kHz PCM Linear, and that rendered the audio but I still got bad audio when exporting to Quicktime. I was however successful in sending to Compressor.
For completeness I’ll try 48 kHz. Thanks for the information.
Bruce Sherwood
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