[Libav-user] How to pass quality scale to mjpeg encoder

Tobias Rapp t.rapp at noa-archive.com
Thu Jan 25 10:25:49 EET 2018


trying to do the equivalent of FFmpeg command-line output option "-q:v 
3" on library level I came up with the following code (error checking 
stripped off):

     AVCodecContext *enc_ctx = NULL;
     const AVCodec *codec = avcodec_find_encoder_by_name("mjpeg");
     int ret;

     enc_ctx = avcodec_alloc_context3(codec);
     enc_ctx->flags |= AV_CODEC_FLAG_QSCALE;
     enc_ctx->global_quality = FF_QP2LAMBDA * 3.0;
     ret = avcodec_open2(enc_ctx, enc_ctx->codec, NULL);

Unfortunately it doesn't seem to have any effect on the output image 
size. Is there something obvious that I'm missing?


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