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• Raspberry Pi : how to configure audio sampling rate in ALSA, ffmpeg, mp3 encoding pipeline

  30 janvier 2014, par user3252022

  I have a Pi with the camera module and a USB sound card. The intent is to use this combination to generate the MPEG2-TS segments for HTTP Live Streaming (Apple's HLS.)

  raspivid -ih -e -w 1280 -h 720 -fps 25 -vf -hf -t 0 -b 1800000 -o - | \
  
  ffmpeg -y \
  
    -i - \
  
    -ac 1 \
  
    -f alsa -ar 22050 -i hw:0,0 \
  
    -c:v copy \
  
    -c:a libshine -strict -2 \
  
    -map 0:0 -map 1:0 \
  
    -f ssegment \
  
    -segment_list_entry_prefix live/ \
  
    -segment_time 10 \
  
    -segment_format mpegts \
  
    -segment_list "$base/live.m3u8" \
  
    -segment_list_size 20 \
  
    -segment_list_flags +live \
  
    -segment_list_type m3u8 \
  
    -segment_wrap 200 \
  
    live/%08d.ts"

  The above basically works. The heavy lifting of H.264 video encoding is done in hardware. However, MP3 encoding in software brings the ARM core to its knees. The option :

  -f alsa -ar 22050 -i hw:0,0

  is intended to lighten the CPU loading by reducing the ALSA audio sampling rate - from the 48kHz default down to 22.05kHz. The sampling rate, however, won't budge to anything below 44.1kHz.

  Any idea what I'm doing wrong ? Why can't I tell ALSA to sample at 22.05kHz (or 8kHz for that matter ?)

  Here's an excerpt output from running the encoding pipeline :

  ffmpeg version N-60125-g4b8c599 Copyright (c) 2000-2014 the FFmpeg developers
  
    built on Jan 29 2014 10:16:02 with gcc 4.6 (Debian 4.6.3-14+rpi1)
  
    configuration: --enable-gpl --enable-nonfree --enable-libshine
  
    ...   
  
  Input #0, h264, from 'pipe:':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: h264 (High), yuv420p, 1280x720, 25 fps, 25 tbr, 1200k tbn, 50 tbc
  
  Guessed Channel Layout for  Input Stream #1.0 : mono
  
  Input #1, alsa, from 'hw:0,0':
  
    Duration: N/A, start: 1391066215.835499, bitrate: 705 kb/s
  
      Stream #1:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
  
      ...

• ffmpeg drops the moov atom when coverting mp4 to ogg, or flv, webm

  31 janvier 2014, par user1370897

  I'm using processor qtfaststart and the gem paperclip-ffmpeg in Rails to convert an mp4 file to either ogg, webm, or flv. However, I haven't had any success converting the mp4 file to these formats for streaming purposes because the moov atom gets dropped (converting mp4 to mp4 keeps its moov atom though*).

  I did a $ qtfaststart -l on the original mp4 file and I get this :

  ftyp (24 bytes)
  
  moov (5691 bytes)
  
  free (399309 bytes)
  
  mdat (12312760 bytes)

  Which shows me that the mp4 file has an moov atom in there. The command that paperclip-ffmpeg is executing is something like this :

  $ ffmpeg -i ~/Movies/VID_20140119_134445.mp4 -acodec libvorbis -ac 2 -ab 96k -ar 44100 -s 640x360 -y ~/tmp/iguana.webm

  However, doing a qtfaststart on the new file (iguana.webm) I get the following :

  $ qtfaststart -l ~/tmp/iguana.webm 
  
  moov atom not found, is this a valid MOV/MP4 file?
  
  Traceback (most recent call last):
  
  File "/usr/local/bin/qtfaststart", line 5, in <module>
  
  pkg_resources.run_script(&#39;qtfaststart==1.8&#39;, &#39;qtfaststart&#39;)
  
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 489, in run_script
  
  self.require(requires)[0].run_script(script_name, ns)
  
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 1214, in run_script
  
  exec script_code in namespace, namespace
  
  File "/Library/Python/2.7/site-packages/qtfaststart-1.8-py2.7.egg/EGG-INFO/scripts/qtfaststart", line 17, in <module>
  
  
  
  File "build/bdist.macosx-10.9-intel/egg/qtfaststart/command.py", line 44, in run
  
  File "build/bdist.macosx-10.9-intel/egg/qtfaststart/processor.py", line 65, in get_index
  
  File "build/bdist.macosx-10.9-intel/egg/qtfaststart/processor.py", line 106, in _ensure_valid_index
  
  qtfaststart.exceptions.FastStartException
  
  </module></module>

  I've also tried adding the option -movflags faststart to the command ffmpeg but ffmpeg still keeps dropping the moov atom to the output file.

  I'm using Rails 4, paperclip-ffmpeg 1.0.1, ffmpeg 2.1.3 Built on Jan 28 2014. Any help would be greatly appreciated.

• ffmpeg drops the moov atom when coverting mp4 to ogg, flv, or webm

  31 janvier 2014, par user1370897

  I'm using processor qtfaststart and the gem paperclip-ffmpeg in Rails to convert an mp4 file to either ogg, webm, or flv. However, I haven't had any success converting the mp4 file to these formats for streaming purposes because the moov atom gets dropped (converting mp4 to mp4 keeps its moov atom though*).

  I did a $ qtfaststart -l on the original mp4 file and I get this :

  ftyp (24 bytes)
  
  moov (5691 bytes)
  
  free (399309 bytes)
  
  mdat (12312760 bytes)

  Which shows me that the mp4 file has an moov atom in there. The command that paperclip-ffmpeg is executing is something like this :

  $ ffmpeg -i ~/Movies/VID_20140119_134445.mp4 -acodec libvorbis -ac 2 -ab 96k -ar 44100 -s 640x360 -y ~/tmp/iguana.webm

  However, doing a qtfaststart on the new file (iguana.webm) I get the following :

  $ qtfaststart -l ~/tmp/iguana.webm 
  
  moov atom not found, is this a valid MOV/MP4 file?
  
  Traceback (most recent call last):
  
  File "/usr/local/bin/qtfaststart", line 5, in <module>
  
  pkg_resources.run_script(&#39;qtfaststart==1.8&#39;, &#39;qtfaststart&#39;)
  
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 489, in run_script
  
  self.require(requires)[0].run_script(script_name, ns)
  
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 1214, in run_script
  
  exec script_code in namespace, namespace
  
  File "/Library/Python/2.7/site-packages/qtfaststart-1.8-py2.7.egg/EGG-INFO/scripts/qtfaststart", line 17, in <module>
  
  
  
  File "build/bdist.macosx-10.9-intel/egg/qtfaststart/command.py", line 44, in run
  
  File "build/bdist.macosx-10.9-intel/egg/qtfaststart/processor.py", line 65, in get_index
  
  File "build/bdist.macosx-10.9-intel/egg/qtfaststart/processor.py", line 106, in _ensure_valid_index
  
  qtfaststart.exceptions.FastStartException
  
  </module></module>

  I've also tried adding the option -movflags faststart to the command ffmpeg but ffmpeg still keeps dropping the moov atom to the output file.

  I'm using Rails 4, paperclip-ffmpeg 1.0.1, ffmpeg 2.1.3 Built on Jan 28 2014. Any help would be greatly appreciated.