[mythtv] Re: Software AC3 decoding when watching TV
Marcus Metzler
mocm at mocm.de
Wed Dec 15 11:52:40 UTC 2004
>>>>> "Tj" == Tj <htpc at treblid.dyndns.org> writes:
Tj> Sorry for the late reply.. was trying to figure out how to
Tj> actually record a short clip.
>> I think this http://liba52.sourceforge.net/ should be installed
>> so ffmpeg can decode ac3.
>>
>>
>>
Tj> I did have that installed - via an RPM for mplayer to play
Tj> ac3... Myth also has libavcodec, does it uses that or uses the
Tj> liba52.so? It seems to use the internal libavcodec...
Tj> If I start and stop mythbackend mythfrontend enough times, I
Tj> actually got AC3 sound working!!!
Tj> a52_decode_frame in libs/libavcodec/a52dec.c only works when
Tj> buf_size is 1024. Anything else there's no sounds..
>> Depends. AC3 should be in privete_stream_1 PES packets in TS
>> stream. At least in DVB and American ATSC. This is where
>> ffmpeg searches for it, see mpegps_read_packet and
>> mpegps_read_pes_header. What do you mean with "startcode"?
>>
>>
>>
Tj> startcode is some variable used by the mpegps_read_pes_header
Tj> function (line 1359: libs/libavformat/mpeg.c). It's called by
Tj> mpegps_read_packet (line 1500: libs/libavformat/mpeg.c). For
Tj> Australia Channel TEN, the AC3 APID has a startcode of 0x1c0,
Tj> which is then assigned the codec_id of CODEC_ID_MP2... (AC3
Tj> has a startcode of 0x80)..
Tj> Also, since it's a ts stream, shouldn't
Tj> libs/libavformat/mpegts.c be used instead?
>> Do you have a bit of stream somewhere? I could take a look.
>>
>>
>>
Tj> you can get it here at http://treblid.dyndns.org/2guys.nuv
Tj> (approx 20MB). Pls tell me if it doesn't work.....
This doesn't look like a TS and I could not find any audio, but I only
downloaded 1MB.
Marcus
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| Dr. Marcus O.C. Metzler | |
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