Marcus Metzler wrote:
Damn. It's clearer after I looked at your email and look at code again. I'm sorta preparing for my holiday so I can't work on this anymore (and I got AC3 unorthodoxically working anyway).. :( I am getting long winded again.. :(AC3 in an MPEG stream, either trnsport or program stream, is packaged in private stream 1 PES packets. Those start with 0x00 0x00 0x01 0xbd
There are private streams for AC3, LPCM and DTS are defined by the DVD
specifications. They call for an additional header inside the PES
payload (not the PES header). For AC3 it is a for byte header
containing the AC3 id (0x80 - 0x87), the number of AC3 frames in the
payload ( 1 byte) and a two byte pointer pointing to the first frame
in the payload.
One more question, if you don't mind and have the time to teach me. Could there a spec diff as to how AC3 audio is "packaged" in ATSC and DVB? Or, as I begin to realise finally, my system is somehow f**ked up and designed to torture/kill me?
in libs/libavformat/mpeg.c approx line: 1461 in function mpegps_read_pes_header does exactly what you mentioned.
if (startcode == 0x1bd) {
if (len < 1)
goto redo;
startcode = get_byte(&s->pb);
len--;
if (startcode >= 0x80 && startcode <= 0xbf) {
// audio: skip header
if (len < 3)
goto redo;
get_byte(&s->pb);
get_byte(&s->pb);
get_byte(&s->pb);
len -= 3;
}
}For my broadcasts, what immediately comes after 0x00 0x00 0x00 0xbd is not 0x80. It's some arbitary number which follows no apparant pattern to me..
There will be a problem for me if I call "startcode = get_byte (&s->pb)", decrement the len var and then realised I did not get the range I want. because at the end of this function, I assign pstart_code to whatever comes after 0x00 0x00 0x00 0xbd, which appears to be random (not tested throughly).
Everything else in myth expects a 0x80 after 0x00 0x00 0x00 0xbd, but my mythbox doesn't do that, causing mythfrontend to crash as it's not expecting that as a startcode.
Without seeing 0x80, I can't really be sure that the private stream I'm handling is actually AC3 rite? How save is it to skip this block of code? (as I am trying to figure how to prevent audio buffer underrun issues when I switch channels between different codecs)
Is this a computer hardware, TV antenna issue or software issue? Is this a bad packet caused by a faulty/lousy antenna?
I am having clear reception in all SDTV channels.. (HDTV video is breaking up occasionally).
Regards.
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