I am trying to convert the audio of an mp4 video file from 32-bit audio to 16-bit linear PCM audio. I want to keep the video unchanged. I set ffmpegx's video codec to "Passthrough (ffmpeg)", checked "encode video", set audio to "PCM DV" and encoded. The resulting file does not display the video (shows a correctly-sized size black or white screen). By the file size and clip properties, it appears to have a video track.

What is the original clip format, you ask? Good question. The original video clip came off a Flip Mino camera. Quicktime plays the video clip fine and shows the original clip's info as AVC coding, 1280x720, millions of colors, with AAC mono audio. When imported into FCP, the FCP clip properties show the video as H.264 (and the clip video displays fine in FCP), with 32-bit floating point audio (which will not play without rendering in the FCP timeline).

The encoded clip from ffmpegx has an .avi extension. In Quicktime, the video is black. In FCP, the video shows as white. Quicktime info shows it to be H.264 format, 1280x720. millions of colors, with 16-bit integer little endian audio. The clip properties in FCP show as H.264, 1280x720, audio properties show as 16-bit integer, and audio plays back fine with no rendering.

I'm trying to avoid exporting and rematching all my audio tracks from the original clips; also trying to avoid the time and unnecessary step of re-encoding all the video (since FCP7 handles the original video fine.) But I am stuck and perplexed. Any ideas?

FFmpegx process info is:

FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
Mac OSX universal build for ffmpegX
libavutil version: 49.0.0
libavcodec version: 51.9.0
libavformat version: 50.4.0
Tue Jan 19 21:25:10 CST 2010
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/mac/Movies/FLIP VIDEOS/HOUSETOUR/MEDIA/first.MP4':
Duration: 00:00:16.1, start: 0.000000, bitrate: 10449 kb/s
Stream #0.0(jpn), 30.00 fps(r): Video: h264, yuv420p, 1280x720
Stream #0.1(jpn): Audio: aac, 44100 Hz, stereo
Output #0, avi, to '/Users/mac/Movies/FLIP VIDEOS/HOUSETOUR/MEDIA/first.MP4.ff.avi':
Stream #0.0, 30.00 fps(c): Video: h264, yuv420p, 1280x720, q=2-31
Stream #0.1: Audio: pcm_s16le, 44100 Hz, stereo, 1411 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Stream #0.1 -> #0.1
bench: utime=0.105s
video:20399kB audio:2776kB global headers:0kB muxing overhead 0.157379%
Encoding completed on Tue Jan 19 21:25:12 CST 2010