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• How can i decode an mp3 and encode it as aac with ezstream

  8 avril 2015, par Roberto Arosemena

  This is my current ezstream config

  <ezstream>
  
     <url>http://localhost:8000/test</url>
  
     <sourcepassword>password</sourcepassword>
  
     <format>MP3</format>
  
     <filename>playlist.m3u</filename>
  
     <reencode>
  
        <enable>1</enable>
  
        <encdec>
  
           <format>MP3</format>
  
           <match>.mp3</match>
  
           <decode>madplay -b 16 -R 44100 -S -o raw:- "@T@"</decode>
  
           <encode>lame --preset cbr 32 -r -s 44.1 --bitwidth 16 - -</encode>
  
        </encdec>
  
     </reencode>
  
  </ezstream>

  It’s mounting to an icecast server, its decoding and encoding mp3 to a lower bitrate, I’m trying to encode it to aac instead of mp3 in hopes that the quality improves as i heard that aac is better than mp3 for lower bitrates.

  What i would like to know is if i can use an aac encoder such as FFmpeg instead of the lame mp3 encoder and get an aac to the end user instead of mp3, if so what parameters should i pass to FFmpeg so that it works with my current config.

• Anomalie #2855 : mauvais traitement du signe par textwheel

  9 août 2014, par cedric -

  Coquille dans le test, corrigée par http://zone.spip.org/trac/spip-zone/changeset/84111
  Si on dit que les < doivent être échappés dans la mesure du possible, le patch suivant semble faire le boulot sans casser aucun autre test.
  Mais est-ce que ça en vaut vraiment la peine ?

  Index : wheels/spip/spip.yaml
  ===================================================================
  
  — - wheels/spip/spip.yaml       (revision 83994)
  +++ wheels/spip/spip.yaml       (working copy)
  @@ -183,3 +183,9 @@
     match : ["\x1\x1", "\x1\x2", "\x1\x3", "\x1\x4"]
     replace : [’’, ’’, ’_’, ’-’]
     type : str
  +
  +echapg-—chevron-ouvrant :
  +  #if_str : "
  &lt;script&quot; <br />
  
  +  type: preg<br />
  
  +  match: &quot;/&lt;([^&gt;&lt;]*)(?=&lt;|$)/Uims&quot; <br />
  
  +  replace: &quot;&amp;amp;lt;$1&quot; <br />
  
  &lt;/pre&gt;

• Can I know which byte range to read from a remote mp4 file for FFMpeg to decode a keyframe ?

  12 octobre 2023, par db9117

  I need to decode a of keyframe of a video file (mp4, h264 encoded). I know the timestamp of the keyframe I want to extract/decode. I want to minimize amount of data being read in memory. For this, I need to know beforehand exactly the minimal byte range I would require that encompasses this keyframe. How do I know what is the minimal byte range in the whole mp4 byte stream I need to read in order to be able to decode the keyframe ?

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  I currently find the appropriate keyframe in the index_entries contained in the header. I get its byte position (pos attribute) and timestamp (timestamp attribute). I calculate the range as follows :

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  startBytes : minimum of :

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  1. the pos of the keyframe

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  2. the pos of the nearest index entry in the audio stream happening at or before the keyframe's timestamp.

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  This way when it's decoding the frame, if it also needs the audio content for demuxing, it would have it.

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  endBytes : maximum of :

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  1. the pos of the next frame in the video stream's index, after the keyframe

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  2. the pos of the next frame in the audio stream's index after the timestamp of the wished keyframe.

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  This way I know that I have everything up until the next frame in the index, which theoretically should be enough to decode the keyframe only.

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  I then read the appropriate byte range.

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  When I try to decode the frame, I run in a loop until I succeed :

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  • avcodec_read_frame

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  • avcodec_send_packet

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  • avcodec_receive_frame

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  I ignore AVERROR(EAGAIN) errors.

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  avcodec_receive_frame fails multiple times with error AVERROR(EAGAIN) which I ignore, until it fails saying that the memory it wants to read isn't available (wants to read after endBytes). I explicitly tell it to fail if it wants to read more than it has already read.

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  Note : for other keyframes at other positions in other videos, it sometimes succeeds (probably because the range is big enough by chance), but it fails more often than not.

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  My question is : Why is the end of the range not enough to be able to decode only the one keyframe ? Is there any way to more precisely calculate the exact range in bytes I would need in order to decode a particular keyframe ?

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