On 25.01.2018 09:25, Tobias Rapp wrote:
Hi,
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?
Answering myself: Apparently setting the encoder option is not
sufficient for mjpeg. The encoding quality has to be set for each frame
that is passed to the encoder.
Example:
frame->quality = enc_ctx->global_quality;
frame->pict_type = AV_PICTURE_TYPE_NONE;
ret = avcodec_send_frame(enc_ctx, frame);
if (ret < 0) {
// ...
}
Looks weird but seems to work.
Regards,
Tobias
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