Hi, Thanks for all your responses, it makes things clearer. So if I understand, I can't encode video without losing quality (the same with decoding, but I don't actually have problems with decoding). But I can't skip decoding for processing reasons. So how to define the encoding tweaks which will minimize the lost of quality ? Is there a function like AVOutputFormat* defineBestDecodeSettings(AVPacket *pkt, enum AVQuality flags); ?
Sincerely,Guillaume Bersac237bis rue de Pessac33000 Bordeaux06.65.30.89.43 > Date: Sun, 23 Jun 2013 23:49:17 +0300 > From: [email protected] > To: [email protected] > Subject: Re: [Libav-user] What define the quality of a decoded video > > On Fri, Jun 21, 2013 at 5:45 PM, Guillaume Bersac <[email protected]> wrote: > > HI, > > > > I have a basic .avi video. I decode it, reencode it using the same type of > > encoder without modifying the decoded data and finally I save it on one file > > of my computer. The saved video has a good framerate but it had lost a lot > > of quality in the process (it's now with a lot of pixel). I kwon that the > > image has been decoded without losing quality. The lost of quality appeared > > during the decoding and saving process. > > What define the quality of a decoded video ? > > > > Thanks, > > Guillaume Bersac > > 237bis rue de Pessac > > 33000 Bordeaux > > 06.65.30.89.43 > > The quality was lost because of re-encoding. Video encoders involve > irreversible transformations, e.g. quantization. Applying this kind of > transformation several times may easily result in bad visual. > > Luckily, you don't need to go through this process if your goal is to > store some video file in a different format. ffmpeg accepts "-vcodec > copy" parameter, which will bypass decoding and re-encoding, and keep > the quality of the original. Same can be easily achieved > programmatically using libavformat and libavcodec, if you are writing > your program (implied by your posting to the libav-user list, and not > to ffmpeg-user list). > > Note however that not all container formats are compatible with all > codecs, so in some use cases "-vcodec copy" is invalid. > > Sincerely, > Alex > _______________________________________________ > Libav-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/libav-user
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