hi all, i have an issue: i'm using "avidemux" which is a video encodind software that includes obviously an audio encoder (LAME): when I encode a video, i get a different size output file (few bytes),
ok, thank you, but there is some way to know if dithering is the cause of this?
if it is so, why do it affects only ABR and not CBR?
Quote from: webpower on 09 April, 2014, 06:37:12 PMok, thank you, but there is some way to know if dithering is the cause of this?I'd say, try avidemux but encode to WAV or a lossless codec and check the output files for differencesQuoteif it is so, why do it affects only ABR and not CBR?Because if the length doesn't change (or only a little bit) CBR produces the same file size. However, with ABR, there is a part of the encoder that tries to decide which blocksize should be used, and that algorithm could be influenced by dither. It might choose a higher or lower bitrate for one or a few blocks.
yes, but i haven't undertood why it changes for every execution with all unchanged, no one thing i have changed.
Quote from: webpower on 12 April, 2014, 10:46:33 AMyes, but i haven't undertood why it changes for every execution with all unchanged, no one thing i have changed.You haven’t answered whether or not you are applying dither. If yes, as said above, dither is random and therefore will not be consistent (assuming a competent algorithm).
Decode the output to wav, then do it again and see if the samples are identical or not.
What tool did you use to check that they were identical ?And I did mean decode. Wav is uncompressed pcm.
Again, everything is pointing towards dither.Even CBR would not produce identical audio under that condition – only size. Did you ever bit-compare the actual audio of the CBR ones?
ooh, i'm just stating that also with LAME CBR they get different output file for every execution, but they have only the same size, WTF