How to convert a flac-extracted album to aac? this will lose quality but aac files are more compact and I don’t need the super extra audiophile quality.

Assume there’s a .flac file and corresponding .cue file for the entire album.

shnsplit can do it in one fell swoop, just ensure you have shnsplit and fdkaac installed and then:

shnsplit -f file.cue -t %n-%t file.flac -o 'cust ext=m4a fdkaac -I -m 5 - -o %f'

These mkv files have h.265 hevc video which my media player can’t read, so I’d like to convert only the video stream to h.264, while leaving all other streams (2 audio tracks in aac, 2 subtitle tracks) intact.

ffmpeg -i some-x265-video.mkv -map 0 -c:v libx264 -c:a copy /tmp/x264-version.mkv

This was used to resync a file whose audio was consistently 1.75 seconds behind the video track. The resulting file also contains the first 2 subtitle tracks from the original file.

vconv -i $IFILE -itsoffset 00:00:01.75 \
 -i $IFILE \
 -i $IFILE \
 -i $IFILE \
 -map 1:0 \
 -map 0:1 \
 -map 2:2 \
 -map 3:3 \
 -acodec copy -vcodec copy -scodec copy \
 sync.mp4
 ``

Sources were [here][1].

 [1]: http://lzone.de/fix%20async%20video%20with%20ffmpeg

avconv replaces the venerable ffmpeg. It can be used to convert videos for the iPhone quite easily.

apt-get install avconv libavcodec-extra-53 libx264-123 x264

then run this script:

avconv -i input-file.mp4 \
    -vcodec libx264 -vprofile high \
    -t 30 \
    -preset slow \
    -b:v 1000k -maxrate 1000k \
    -bufsize 2000k -vf scale=1136:474 \
    -acodec libvo_aacenc -b:a 192k output_file.mp4

Another example. This uses time to calculate elapsed time, also nice and ionice to try to reduce impact on system resources. It forces downsampling to two audio channels (-ac 2), useful if the source audio stream is in e.g. 5.1 format.

time ionice -c 3 nice -20  avconv  -i whatever.avi  \
-vcodec libx264 -vprofile high -preset slow -b:v 1000k\
 -maxrate 1000k -bufsize 2000k  -acodec libvo_aacenc \
-ac 2 -ab 112k output.mp4

A final example which forces a specific aspect ratio. The source video had the correct pixel dimensions but a bad aspect ratio was encoded in the original file (and was carried over to the recoded one), making it look squished.

avconv  -i input.avi  -vcodec libx264 -aspect 16:9 \
-vprofile high -preset slow -b:v 1900k -maxrate 1900k \
-bufsize 3800k  -acodec libvo_aacenc -ac 2 -ab 112k output-iphone.mp4