Impossible to set quality for libvorbis

[shadowlmd]

I am trying to write Ogg Vorbis files with the following code:

        output = av.open(str(outfile), "w")
        out_stream = output.add_stream("libvorbis", rate=audio_stream.rate)
        out_stream.options["global_quality"] = "9"  # https://ffmpeg.org/ffmpeg-codecs.html#Options-21

        for packet in container.demux(audio_stream):
            for frame in packet.decode():
                pkt = out_stream.encode(frame)
                if pkt:
                    output.mux(pkt)

        for pkt in out_stream.encode():
            output.mux(pkt)

        output.close()

Everything works, but I get an ogg vorbis file with bitrate ~112 kbps, definitely not q9. I also tried to add out_stream.qscale = True, but then the bitrate of the output file is ~ 65 kbps.

Is it a bug or I am doing something wrong? How do I set quality for libvorbis encoder?

[WyattBlue]

In C FFmpeg, you need to do:

// Set global_quality on the codec context
// Values are on a 0–10 scale, multiplied by FF_QP2LAMBDA
codec_ctx->global_quality = 4 * FF_QP2LAMBDA;
codec_ctx->flags |= AV_CODEC_FLAG_QSCALE;

We probably should expose global_quality in CodecContext

[WyattBlue]

#2246 should fix this

[shadowlmd]

That was fast. Thank you!