Quoting Danny Hong (2024-09-09 19:45:57) > Thanks for the patch set! Ran some initial tests and here are some > findings: > > 1. Tested using the HTM ref SW encoded bitstreams; the HTM encoded 2 layer > MV-HEVC elementary streams are decoded by both the HTM decoder and ffmpeg, > and both resulted in the same decoded pixels for both views. > > 2. Tested with the iPhone captured sample videos (some samples are > available from > https://blog.frame.io/2024/02/01/how-to-capture-and-view-vision-pro-spatial-video/). > To decode using the HTM decoder, converted the .mov file to .hevc > elementary stream (using "ffmpeg -view_ids -1 -i sample.mov -vcodec copy > sample.hevc"). The iPhone captured MV-HEVC seems to be non-conformant as
Note that -view_ids is a decoder option and does nothing with streamcopy. Also, that option is intended for API users, with ffmpeg CLI you should be using view specifiers instead. > for the very first AU we have the following NAL units: prefix SEI (layer ID > 0), CRA (layer ID 0), prefix SEI (layer ID 0), CRA (layer ID 1). Based on > Section 7.4.2.4.4 of the HEVC spec, a prefix SEI with layer ID 0 indicates > a new AU, so the bitstream is not conformant for the 2 layer case. The > reference HTM decoder seems to be tolerant to this and correctly decodes > the "non-conformant" elementary stream, but ffmpeg does not. However, > ffmpeg does decode the .mov container file correctly as each AU is > correctly passed to the decoder as a video sample. Aside from this > con-conformance issue, both the HTM decoder and ffmpeg seem to produce > pixel exact views. For the view by view comparison, I had to manually skip > some initial frames output by the HTM decoder, as ffmpeg did not output > some of the first few views/frames. > > 3. When ffmpeg skips some of the decoded views for output, I think it > makes sense to skip both views of an AU (when both views are being > output)? Currently one view from an AU can be skipped without skipping its > corresponding other view. To avoid some of the views from being skipped, I > had to use the "-vsync 0" option for my tests. When I use this option, I > see the following warning: "Application provided invalid, non monotonically > increasing dts to muxer in stream 0: 1 >= 1". This seems due to both views > of an AU having the same DTS, which is expected. Use view specifiers to split the views into their own streams. I do not want too much multiview-speficic logic into ffmpeg CLI, as it is a rather obscure feature. -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
