Hi, On Sat, Jan 2, 2016 at 3:23 PM, Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
> On Fri, Jan 1, 2016 at 8:07 AM, Ganesh Ajjanagadde <gajja...@mit.edu> > wrote: > > Hi all, > > > > Motivated by a remark by Ronald: > > https://ffmpeg.org/pipermail/ffmpeg-devel/2016-January/186200.html, > > this is a request for comment on disabling compile time tablegen for > > cbrt if the total cycle count < 200000. Note that cbrt tables are only > > used in aacdec. > > To start some effort towards a more principled understanding of the > costs of runtime table initialization, I did some benchmarks. > Note: I am not familiar with avcodec, so I don't know if this reflects > correctly the static vs dynamic cost. > file: ~/samples/aac/al04_44.mp4 > stream_loop: 100 > number of calls of avcodec_decode_audio4: 35956 > cost per call (avcodec_decode_audio4): > 834030 decicycles in decode_audio4, 1 runs, 0 skips > 556200 decicycles in decode_audio4, 2 runs, 0 skips > [...] > 177365 decicycles in decode_audio4, 16384 runs, 0 skips > 177059 decicycles in decode_audio4, 32768 runs, 0 skips > decoding cost: 17706*35956 = 636,636,936 cycles > duration: 832.55 seconds > cost per second of audio: 764,683 cycles > cost of table init: 200,000 cycles > fraction: 0.26 > > So in a clip of n seconds duration, the relative overhead of dynamic > initialization of these cbrt tables is 0.26/n. For a more concrete > number, say a clip is of 180 seconds duration, then the overhead is > 0.26/180 = 0.15%. What if I only want to play the first 3 second of 1000 clips by calling ffmpeg.exe in a shell script? E.g. for fingerprinting. The number of use cases you cover needs to be more than just playback, ffmpeg can do much more than just that. Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
