Unexplained freeze/hang from gst-omx omxh264enc on Raspberry Pi 3

Graham Leggett minfrin at sharp.fm
Tue Nov 15 01:34:00 UTC 2016 

Hi all,

I am having some strange behaviour from gst-omx and the omxh264dec/omxh264enc elements that I am trying to get to the bottom of, the pipeline seems to hang at random points and I am trying to get to the bottom of why.

I have recorded an MPEG transport stream containing h264 video that originates from DVB-T2, and am trying to transcode this with an element that has the effect of “decodebin ! encodebin”. The stream is demuxed and decoded with omxh264dec, and then reencoded with omxh264enc and remuxed before being written to an HLS stream.

My problem is that each time this recorded MPEG transport stream is transcoded, the pipeline freezes/hangs at a different point in time. I would expect the file to freeze/hang in the same place, but it doesn’t do so.

When it freezes the pipeline, omxh264enc says the following and then goes silent: 

0:05:26.921029963  2774 0x73101d50 DEBUG            omxvideoenc gstomxvideoenc.c:1692:gst_omx_video_enc_drain:<omxh264enc-omxh264enc0> Draining component
0:05:26.921240325  2774 0x73101d50 DEBUG            omxvideoenc gstomxvideoenc.c:1738:gst_omx_video_enc_drain:<omxh264enc-omxh264enc0> Waiting until component is drained
0:05:26.922070629  2774 0x75714ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:05:26.924129253  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:753:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Handling buffer: 0x00000480 0
0:05:26.924239825  2774 0x75714ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:05:26.924242950  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:762:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Finished frame: ok
0:05:26.924531385  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:770:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Read frame from component
0:05:26.924573780  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:753:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Handling buffer: 0x00000490 0
0:05:26.924627790  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:762:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Finished frame: ok
0:05:26.924861589  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:770:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Read frame from component
0:05:26.924899402  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:753:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Handling buffer: 0x00000430 1482599921
0:05:26.924961536  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:586:gst_omx_video_enc_handle_output_frame:<omxh264enc-omxh264enc0> Handling output data
0:05:26.925675123  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:762:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Finished frame: ok
0:05:26.926104754  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:770:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Read frame from component
0:05:26.926179857  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:753:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Handling buffer: 0x00000001 1482639921
0:05:26.926242565  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:762:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Finished frame: ok
0:05:26.926448604  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:770:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Read frame from component
0:05:26.926489698  2774 0x73145400 DEBUG            omxvideoenc gstomxvideoenc.c:810:gst_omx_video_enc_loop:<omxh264enc-omxh264enc0> Drained
0:05:26.926540010  2774 0x73101d50 DEBUG            omxvideoenc gstomxvideoenc.c:1740:gst_omx_video_enc_drain:<omxh264enc-omxh264enc0> Drained component

omxh264dec keeps running, until eventually, sometimes within a second, sometimes many seconds later, omxh264dec also freezes and goes silent as follows:

0:06:05.580576707  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.583004391  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.585423220  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.587669864  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.591000038  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.591114776  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2185:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Starting task
0:06:05.591252691  2581 0x74d018f0 DEBUG            omxvideodec gstomxvideodec.c:1570:gst_omx_video_dec_loop:<omxh264dec-omxh264dec0> Component signalled EOS
0:06:05.591313316  2581 0x74d018f0 DEBUG            omxvideodec gstomxvideodec.c:1590:gst_omx_video_dec_loop:<omxh264dec-omxh264dec0> EOS
0:06:05.605895926  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.606009936  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2185:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Starting task
0:06:05.606143997  2581 0x74d018f0 DEBUG            omxvideodec gstomxvideodec.c:1570:gst_omx_video_dec_loop:<omxh264dec-omxh264dec0> Component signalled EOS
0:06:05.606203319  2581 0x74d018f0 DEBUG            omxvideodec gstomxvideodec.c:1590:gst_omx_video_dec_loop:<omxh264dec-omxh264dec0> EOS
0:06:05.606916541  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2178:gst_omx_video_dec_handle_frame:<omxh264dec-omxh264dec0> Handling frame
0:06:05.609172247  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2457:gst_omx_video_dec_drain:<omxh264dec-omxh264dec0> Draining component
0:06:05.609289433  2581 0x75614ac0 DEBUG            omxvideodec gstomxvideodec.c:2462:gst_omx_video_dec_drain:<omxh264dec-omxh264dec0> Component not started yet

I have a number of questions:

- Has anyone encountered inconsistent pipeline freezes with omxh264enc?

- What does "Draining component” do? It appears to be called from gst_omx_video_enc_finish(), but I cannot figure out why finish is being called on the encoder or what triggered it.

- Are there any known bugs in omxh264enc that would cause it to stop encoding for any reason (as opposed to being temporarily degraded but still running).

Does anyone have a suggestion on what to try next?

Regards,
Graham
—

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