Eliot Blennerhassett wrote: > Tobin Davis wrote: >> Are there any alsa supported sound cards that do hardware audio decoding >> for MP3/WMA and otehr formats? I'd like to look at the mechanism used >> to connect the cards to the data stream. > > This has come up a couple of times recently. > > Todays answer is that ALSA has no support for getting the encoded data > through to the cards. > > We are interested in this and would like to see it happen because our > cards do support MP2 and MP3 decode and encode in DSP on the cards. > > Applications wanting to use this capability currently must use our HPI > driver directly (the primary example on Linux is Rivendell radio > automation software http://www.rivendellaudio.org) > > One assumption that alsa makes is that a "period" equates to a fixed > amount of time, and a fixed amount of audio data. This is not the case > for Variable bitrate mpeg etc. And even with fixed bitrate, the bits > per sample is fractional E.g. 128kbps/44.1k = 2.90249... bits per sample > frame. > > One of the two assumptions about the period would have to be relaxed to > allow alsa to maybe work with compressed data. Probably the time one. > I.e. a period means the decoder has consumed X bytes, but this doesn't > correspond to any particular amount of time. > Hi, you probably know the workarounds of spdif-passthrough in alsa-enabled applications. Perhpaps these techniques could be of some help. E.g. mplayer padds the missing data with zeroes for AC3/DTS passthrough. My AVR decoder does not seem to mind. http://www.mplayerhq.hu/DOCS/tech/hwac3.txt http://svn.mplayerhq.hu/mplayer/trunk/libmpcodecs/ad_hwac3.c?view=markup Though I guess the zeroes would probably corrupt the MP3 stream. Regards, Pavel. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
