On Sun, 16 Jul 2017, Nicolas George wrote:
Le septidi 27 messidor, an CCXXV, Hans Carlson a écrit :
$ ffmpeg -f s16le -ac 2 -f concat -i concat-raw.txt ...
or
$ ffmpeg -f concat -f s16le -ac 2 -i concat-raw.txt ...
I've tried both and it doesn't work, so I assume it's either not supported
or I'm doing something wrong.
That cannot work, the second -f option is just overriding the first one.
I kind of figured that's what was happening.
You would need to specify the format and options in the concat script
itself, as they could be different for each file. But it is not
implemented yet.
"... not implemented yet"? Does that mean it's currently in the works?
Or just something that has been considered, but no work has been done?
Since PCM is just a sequence of uncompressed samples, you can use the
concat PROTOCOL to join them, and the subfile protocol to extract part
of them. You just need a little arithmetic to convert from timestamp to
octet offset.
I had tried to use subfile, but at the time, was still using it with the
concat DEMUXER. I quickly realized that has the same problem... still
need to specify the -f option twice and only the 2nd one is used. But I
hadn't considered using subfile and the concat PROTOCOL. That does seem
to work... at least with my test case:
$ ffmpeg -f s16le -ac 2 -i
'concat:subfile,,start,5292000,end,47628000,,:file1.raw|subfile,,start,1764000,end,28224000,,:file2.raw'
-codec mp3 test.mp3
To calculate the subfile offset sizes, I multiplied the start/end times by
176400 (which is the filesize=[52920320] / duration=[300.001814]). So,
for file1.raw, inpoint=30 = (176400 * 30 = 5292000) and outpoint=270 =
(176400 * 270 = 47628000).
I checked 200+ PCM (s16le) files and the multiplier was virtually the same
for all of them 176400 (+/- ~0.0005). So is 176400 the "standard"
bytes/sec for PCM (s16le)? In other words, can I just use 176400 as a
fixed number for calculating the subfile offset size, or should I be doing
some other calculation to determine this multiplier?
Since PCM is lossless, you can use the concat FILTER to join them, and
the trim filter (possibly implicitly with -ss and -t) to extract a part.
I previously looked into the concat FILTER, but wasn't sure how to extract
a section from each file. I assume you mean "atrim" in my case and not
"trim".
Combining the concat FILTER and atrim I came up with the following and it
works as well:
ffmpeg -f s16le -ar 44100 -ac 2 -i file1.raw -f s16le -ar 44100 -ac 2 -i
file2.raw -filter_complex '[0:0]atrim=30:270[a1]; [1:0]atrim=10:160[a2];
[a1][a2]concat=n=2:v=0:a=1[a]' -map '[a]' -codec:a mp3 test.mp3
I also tried using -ss/-t as input options for each file instead of
"atrim" and that also works:
ffmpeg -accurate_seek -f s16le -ar 44100 -ac 2 -ss 30 -t 240 -i file1.raw -f
s16le -ar 44100 -ac 2 -ss 10 -t 150 -i file2.raw -filter_complex
'[0:0][1:0]concat=n=2:v=0:a=1[a]' -map '[a]' -codec:a mp3 test.mp3
Thanks for the various options.
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