On 8/2/2020 11:22 AM, Jan Ekström wrote: > On Sat, Aug 1, 2020 at 4:44 PM Jan Ekström <jee...@gmail.com> wrote: >> >>>> At this point I would not like to attempt to figure out how to skip >>>> channel coding units in the AAC decoder >>> >>> Just throw them away? >>> >> >> Very easy to say in words, but I am not sure how simple this is in the >> code. That said, if you are interested in implementing this in the >> decoder, I am not opposed to the idea since in this specific case the >> spec seems to note that 5.1 can be mapped into those channels. >> > > I took a quick look at output_configure in aacdec_template, and it > isn't too clear what's the best way of getting this done. > > The more proper way would seem to be to see if sniff_channel_order > returned a layout, and then proceed to applying a switch/case thing > for request_channel_layout. But more looking into the decoder would be > required to figure out if one can get it done with: > A. Just zero out mappings past the needed coding units. > B. A and resetting the tags count within output_configure (since that > is a parameter received from an outer function) > C. Something else? > > Alternatively, something similar to B could get received by having the > switch/case just before the get_new_frame check, and just overriding > the layout and channels variables. > > The problem is that I'm not sure how well the best working alternative > of these will work: > A. Not at all, since it will attempt to pull in data for 24 channels > but the AVFrame only contains 6. Segfault. > B. Kind of. 24 channels will get allocated, but layout is 5.1. > C. ??? > > I hope this clears up why I'm not too interested in trying to figure > this out right now, since I have just been able to figure out the base > decoding (which is currently everything the decoder supports!) and > downmix through swresample.
As i said, that's fine for now. request_channel_layout implementations are optional and not always feasible (Very few audio codecs truly define a way to implement it, like it's the case of DTS). The decoder's job is to output what the stream contains, and a resampler can take care of everything afterwards should the user want something that's not defined within the bitstream. _______________________________________________ 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".
