Reencoding to mp4 with FFmpeg results in significantly lower volume

Question

For some reason the mp4's I reencode have very low volume.

ffmpeg -i "\"$FILENAME\"" -sameq  -vf "\""movie=/files/logo.png [watermark]; \
[in][watermark] overlay=main_w-overlay_w-10:main_h-overlay_h-10[out]\""" -ac 2 \
-vcodec libx264 -threads 0 -acodec libfaac -async 2 \
"\""$OUTPUT_DIRECTORY/abc$OUTPUTFILENAME"\

I added a few flags to keep the audio in sync, etc.

Answer 1

If the original audio is more than 2 channels, you could be losing some of the volume when you do "-ac 2"

You can try "-acodec copy" unless you have to use libfaac.

I've had mixed success with ffmpeg pan http://ffmpeg.org/ffmpeg-filters.html#pan

You could dry to manually pan your input channels together and add gain there.