Re: [Libav-user] What is correct method to identify streams containing alpha?

[Mark Schafer]

Brilliant thanks Anton. Just to be complete if its codec "139 - Google VP8" then you need to find "libvpx-vp8" and if its "167 - Google VP9" then you need to find "libvpx-vp9". Also you can load a stream with avcodec_open2 and override the codec there instead. On 6/15/2018 7:25 PM, Anton Shekhovtsov wrote: Hi, "libvpx" is not input format, see this for example   AVCodec* pDecoder = avcodec_find_decoder(m_pStreamCtx->codecpar->codec_id);   if(m_pStreamCtx->codecpar->codec_id==AV_CODEC_ID_VP8){     // on2 vp8 does not extract alpha     AVCodec* pDecoder2 = avcodec_find_decoder_by_name("libvpx");     if(pDecoder2) pDecoder = pDecoder2;   } 2018-06-15 3:02 GMT+03:00 Mark Schafer <mscha...@wireframe.biz>: Ahh I think its AVInputFormat *inputFormat =av_find_input_format("libvpx"); avformat_open_input(&pAVFormatContext, dev_name, inputFormat, NULL) On 6/15/2018 11:49 AM, Mark Schafer wrote: OK. Thanks Carl. So you're saying I should always override it with libvpx if the file I'm loading is .webm ? and if you don't mind - how do I override the codec on load ? Is it in AVInputFormat by stipulating the extension and codec_tag ? On 6/15/2018 11:13 AM, Carl Eugen Hoyos wrote: 2018-06-14 23:03 GMT+02:00, Mark Schafer <mscha...@wireframe.biz>: We're trying to integrate ffmpeg 4 with Pyglet. Its all going very well but we have one issue: - If a VP9 (or VP8) file is created using ffmpeg4 from png files with alphas, we get a video file (webm) with alpha internally. (Excellent) - ffmpeg -i image_seq%03d.png -qmin 0 -qmax 50 -crf 5 -b:v 1M output.webm       - The report from this CLI indicates that an alpha has been generated. - Sample webm videos with alpha can be found on this page: https://simpl.info/videoalpha/ - However on playing back we only get the RGB and do not get the alpha unless we override the codec to be 'libvpx'. Yes, this is a known limitation of the native decoder, luckily you have already found the only known work-around - not to use it if you need this feature. If you really want to choose the decoder based on the alpha layer, you can check AV_PKT_DATA_MATROSKA_BLOCKADDITIONAL if the side_data starts with (uint64_t) 1 there is a transparency layer. It is probably simpler to always use the libvpx decoder. Carl Eugen _______________________________________________ Libav-user mailing list Libav-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/libav-user _______________________________________________ Libav-user mailing list Libav-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/libav-user _______________________________________________ Libav-user mailing list Libav-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/libav-user _______________________________________________ Libav-user mailing list Libav-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/libav-user

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