On Wednesday 06 Jul 2016 16:07:17 Stroller wrote: > > On 5 Jul 2016, at 16:54, wabe <[email protected]> wrote: > > > > If you wanna put the audio data into another container without recoding > > it, you can use for example something like that: > > > > ffmpeg -i filename.mp4 -acodec copy filename.m4a > > This has worked. Many thanks for your help. > > I did not actually expect this, as I thought .mp4 and .m4a were the same > thing (see links below) and renaming the .mp4 to .m4a did not have any > effect.
They are not exactly the same thing, in the sense that m4a ought to only have an audio stream in it, but mp4 may have more streams (audio and video). > ffmpeg did, however, seem to do no more than copy the stream (it took only a > second or so), so presumably it has marked the container differently > somehow. See attached, anyone who's interested. If you notice youtube-dl used ffmpeg after it downloaded your file to fix something in the aac bitstream, which it considered 'malformated': [download] Destination: The Bronze Age Collapse, In Our Time - BBC Radio 4- b07fl2qw.mp4 [download] 100% of 40.56MiB in 01:36 [ffmpeg] Fixing malformated aac bitstream in "The Bronze Age Collapse, In Our Time - BBC Radio 4-b07fl2qw.mp4" If you run ffprobe on the partly downloaded mp4 file before youtube-dl completes and has a chance to use ffmpeg, you can compare its output with the 'fixed' mp4 file and then your own m4a audio extract to see what the differences might be. > I appreciate the contributions of all who've replied, > > Stroller. > > > > [1] http://stackoverflow.com/questions/9412384/ > [2] https://en.wikipedia.org/wiki/MPEG-4_Part_14#.MP4_versus_.M4A > [3] https://wiki.jriver.com/index.php/MP4_and_M4A_File_Support -- Regards, Mick
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