On Tue Jul 21 18:08:04 BST 2015, Jim web wrote:
IIRC I always tend to use
-acodec copy -vcodec copy
Hi Jim...
"-c copy" (also "-codec copy" or "-codec: copy")
in fact means "copy all the streams without reencoding";
there exist two elementary streams inside the FLV
container (video+audio), so in this case:
"-c copy" = "-acodec copy -vcodec copy"
(and "-acodec copy"/"-vcodec copy" is a slightly
older wording, though still backwards compatible;
the ffmpeg devs propose we use
"-c:a copy"/"-c:v copy" instead...)
ffmpeg -i foo.flv -c copy -bsf:a aac_adtstoasc foo.mp4
curious to know what the -bsf option choice does.
I'll have a man read. :-)
https://www.ffmpeg.org/ffmpeg-bitstream-filters.html#toc-aac_005fadtstoasc
2.1 aac_adtstoasc
Convert MPEG-2/4 AAC ADTS to MPEG-4 Audio Specific Configuration bitstream
filter.
This filter creates an MPEG-4 AudioSpecificConfig from an MPEG-2/4 ADTS
header and removes the ADTS header.
This is required for example when copying an AAC stream from a raw ADTS
AAC container to a FLV or a MOV/MP4 file.
It turns out this filter is not actually needed
in the lossless remux of FLV to MP4; I remember
reading many moons ago in the "videohelp" forums
that it doesn't hurt including it in the command; I did some
fresh tests with an FFmpeg 2.7.1 win32 binary and indeed
I see no difference with it included or not.
HOWEVER, you should use this audio filter when:
1. an elementary audio stream with the ADTS header
is muxed into the MP4 container:
ffmpeg -loglevel 16 -stats -i EV.h264 -i EA.aac -c copy -bsf:a aac_adtstoasc
AV.mp4
2. you remux losslessly from the MPEG-TS container
to the MP4 one:
ffmpeg -i AV.ts -c copy -bsf:a aac_adtstoasc AV.mp4
(.ts files often the product of ffmpeg recording
AppleHLS live or on-demand streams...)
If you can read Perl, you can see how this filter is
already used in GiP 2.94, if you search
http://git.infradead.org/get_iplayer.git/blob/refs/heads/master:/get_iplayer
for the term: "aac_adtstoasc"
Regards,
Vangelis.
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