Re: ivtv-utils/test/ps-analyzer.cpp: error in extracting SCR?

[Lars Hanisch <dvb@cinnamon-sage.de>]

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Hi,

  Just for completeness, attached is the patch against the subversion 
repository at ivtvdriver.org.

Regards,
Lars.

Am 04.02.2010 08:25, schrieb Hans Verkuil:
> On Thursday 04 February 2010 04:16:03 Andy Walls wrote:
>> On Thu, 2010-02-04 at 01:18 +0100, Lars Hanisch wrote:
>>> Hi,
>>>
>>>    I'm writing some code repacking the program stream that ivtv delivers
>>> into a transport stream (BTW: is there existing code for this?).
>>
>> Buy a CX23418 based board.  That chip's firmware can produce a TS.
>>
>> I think Compro and LeadTek cards are available in Europe and are
>> supported by the cx18 driver.
>>
>>>   Since
>>> many players needs the PCR I would like to use the SCR of the PS and
>>> place it in the adaption field of the TS (if wikipedia [1] and my
>>> interpretation of it is correct it should be the same).
>>>
>>>    I stumbled upon the ps-analyzer.cpp in the test-directory of the
>>> ivtv-utils (1.4.0). From line 190 to 198 the SCR and SCR extension are
>>> extracted from the PS-header. But referring to [2] the SCR extension has
>>> 9 bits, the highest 2 bits in the fifth byte after the sync bytes and
>>> the lower 7 bits in the sixth byte. The last bit is a marker bit (always 1).
>>>
>>>    So instead of
>>>
>>> scr_ext = (hdr[4]&  0x1)<<  8;
>>> scr_ext |= hdr[5];
>>>
>>>    I think it should be
>>>
>>> scr_ext = (unsigned)(hdr[4]&  0x3)<<  7;
>>> scr_ext |= (hdr[5]&  0xfe)>>  1;
>>
>>
>> Given the non-authoritative MPEG-2 documents I have, yes, you appear to
>> be correct on this.
>>
>> Please keep in mind that ps-analyzer.cpp is simply a debug tool from an
>> ivtv developer perspective.  You base prodcution software off of it at
>> your own risk. :)
>>
>>>    And the bitrate is coded in the next 22 bits, so it should be
>>>
>>> mux_rate = (unsigned)(hdr[6])<<  14;
>>> mux_rate |= (unsigned)(hdr[7])<<  6;
>>> mux_rate |= (unsigned)(hdr[8]&  0xfc)>>  2;
>>>
>>>    Am I correct?
>
> Yes, you are correct. I miscounted the bits when I wrote this originally.
> Thanks for reporting this!
>
> Regards,
>
> 	Hans
>
>>
>> I did not check this one, but I would not be surprised if ps-analyzer
>> had this wrong too.
>>
>> Regards,
>> Andy
>>
>>> Regards,
>>> Lars.
>>>
>>> [1] http://en.wikipedia.org/wiki/Presentation_time_stamp
>>> [2] http://en.wikipedia.org/wiki/MPEG_program_stream
>>> --
>>
>>
>> --
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>>
>


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Index: test/ps-analyzer.cpp
===================================================================
--- test/ps-analyzer.cpp	(Revision 4152)
+++ test/ps-analyzer.cpp	(Arbeitskopie)
@@ -194,11 +194,11 @@
 	scr |= (u64)(hdr[2] & 3) << 13;
 	scr |= (u64)hdr[3] << 5;
 	scr |= (u64)(hdr[4] & 0xf8) >> 3;
-	scr_ext = (hdr[4] & 0x1) << 8;
-	scr_ext |= hdr[5];
-	mux_rate = (hdr[6] & 0x7f) << 15;
-	mux_rate |= hdr[7] << 7;
-	mux_rate |= (hdr[8] & 0xfe) >> 1;
+	scr_ext = (unsigned)(hdr[4] & 0x3) << 7;
+	scr_ext |= (hdr[5] & 0xfe) >> 1;
+	mux_rate = (unsigned)(hdr[6]) << 14;
+	mux_rate |= (unsigned)(hdr[7]) << 6;
+	mux_rate |= (unsigned)(hdr[8] & 0xfc) >> 2;
 	if (g_verbose)
 		printf("%lld: pack scr=%lld scr_ext=%3u scr=%lld ns mux_rate=%u\n", pos, scr, scr_ext, scr2ns(scr, scr_ext), mux_rate);