[Libav-user] warning of "[libmp3lame @ 00CAB020] frame_size is too large" while calling avcodec_encode_audio2()

[jettoblack]

zhao0130 wrote
> I am using ffmpeg api to transcode a movie (.mp4 -> .mov). I got a warning 
> while calling avcodec_encode_audio2(): "[libmp3lame @ 00CAB020] frame_size 
> is too large". I believe this should be due to that the frame size of 
> decoding AVCodecContext, 1024, is different from that of encoding 
> AVCodecContext, 1152. The audio codec of the mp4 file is AAC and that of 
> the mov file is MP3. The default of frame size of MP3 seems 1152 and I can 
> not force it to be 1024. I set other parameters such as sample_rate, 
> bit_rate, sample_fmt and channels of encoding AVCodecContext same as those 
> of decoding AVCodecContext. Help will be really appreciated!

You need to use a FIFO for the audio samples.  Each time you get samples
from the decoder, push them into the FIFO.  Whenever the FIFO size is at
least the encoder's frame_size, pull one frame's worth of samples out of the
FIFO into the encoder.  There is audio FIFO code already built into ffmpeg:
http://ffmpeg.org/doxygen/trunk/group__lavu__audio.html

Some audio codecs like PCM have a frame_size of 0.  I use 1024 samples for
those.




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