[mythtv] libcmyth failing to receive HD stream

Chase Douglas chasedouglas.lists at gmail.com
Mon Feb 23 16:37:26 UTC 2009

On Feb 22, 2009, at 8:01 AM, Stuart Morgan wrote:
> On Saturday 21 February 2009 23:39:54 Chase Douglas wrote:
>> I'm working on a separate frontend project using libcmyth and I've
>> been able to generate and play a live tv SD stream from an IVTV card.
>> A few times I've been able to generate and play an HD stream from a
>> pcHDTV-5500 card. However, usually the HD stream playback doesn't
>> work. The frontend keeps requesting bytes (as low as 1 byte), and the
>> backend keeps returning 0.
>> My guess as to why I'm seeing this only on HD streams is that the SD
>> stream from the IVTV card is "always on". There's no lag time between
>> starting a recording and the recording file being available apart  
>> from
>> the backend processes creating the recording. However, a digital
>> recording has to first tune and lock on to the signal before the
>> recording actually starts. I am guessing that my frontend is missing
>> some step between spawning live tv and beginning to request bytes of
>> the stream. I see the following in the backend log:
>> 2009-02-21 17:10:46.739 Preview Error: Previewer file '/home/mythtv/
>> recordings/1840_20090221171043.mpg' is not valid.
>> 2009-02-21 17:10:46.740 Preview Error: Run() file not local: '/home/
>> mythtv/recordings/1840_20090221171043.mpg'
>> 2009-02-21 17:10:46.746 Preview Error: Preview process not ok.
>>                         fileinfo(/home/mythtv/recordings/
>> 1840_20090221171043.mpg.png) exists: 0 readable: 0 size: 0
>> 2009-02-21 17:10:51.531 RingBuf(/home/mythtv/recordings/
>> 1840_20090221171043.mpg): Invalid file (fd -1) when opening '/home/
>> mythtv/recordings/1840_20090221171043.mpg'.
>> 2009-02-21 17:10:51.567 MainServer::HandleAnnounce Playback
>> 2009-02-21 17:10:51.568 adding: mythtv as a client (events: 0)
>> 2009-02-21 17:10:51.580 RingBuf(/home/mythtv/recordings/
>> 1840_20090221171043.mpg) Error: Invalid file descriptor in  
>> 'safe_read()'
>> --- last line repeating indefinitely ---
>> I've run a tcpdump of a MythTV frontend to see what messages it sends
>> back and forth. I see it send on a control port:
>> ANN Playback
>> QUERY_RECORDER IS_RECORDING (backend returns 1)
>> *QUERY_RECORDER IS_RECORDING (backend returns 1)
>> *QUERY_CHECKFILE (backend returns 1 and filename)
>> *QUERY_CHECKFILE (backend returns 1 and filename)
>> Then a new control port and the video streaming port are spawned  
>> and I
>> see:
>> ANN Playback
>> ANN FileTransfer (on the streaming port)
>> And from then on things progress as one would expect, with the new
>> control port requesting blocks and the new streaming port receiving
>> the blocks. My frontend using libcmyth leaves out any of the messages
>> I've starred (*) above. Which, if any, of these messages are  
>> required?
>> Does this explain why I'm having issues with the digital stream, or  
>> am
>> I missing something? Is there something on the event connection,  
>> which
>> I'm not really listening to, that is salient?

As a followup, I've figured out what the issue is. I was not listening  
for the live tv chain update messages on the event connection, so I  
wasn't getting updates and initiating file transfer connections to the  
newer correct recording files. Everything is working normally for me  


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