Re: Error in streamed MPEG4 handling - Movie.pm or Audio::Scan error ?

bpa wrote: 
> Looking at feasibility of an Accuradio plugins and was checking the
> audio streams.
> I've having a problem playing some MPEG-4 streaming URLs. Tests are on a
> Ubuntu system LMS 8.3 (2Jan) 
> 
> It looks like a bug in either LMS MPEG-4 Handling of InitialAudioBlock
> or in Audio::Scan
> 
> Example URL.
> https://d1qg6pckcqcdk0.cloudfront.net/classical2/londonoratorysc_sacredtreasures_07_salvatormundii.m4a
> 
> When downloaded as a file, the file plays OK on both an Receiver (i.e.
> faad MP4->Flc transcode) and a DAC32 (i.e. MP4->aac) 
> 
> When played as an URL
> - no output on Receiver - faad (-q removed) produces an error -
> Duration, speed and channel all are wrong.
> > 
Code:
--------------------
  >   > 
  > Streamed input format  samplerate 22050 channels 0.
  > - file info:
  > ADTS, 1.000 sec, 16 kbps, 44100 Hz
  > 
  > Error: Bitstream value not allowed by specification
  > 
--------------------
> > 
> 
> - DAC32 error  following error is logged 
> > 
Code:
--------------------
  >   > 
  > [22-01-02 16:58:25.3427] Slim::Player::Squeezebox2::statHandler (156) Error: 7c:9e:bd:2b:52:94: Decoder does not support file format, code 0
  > 
--------------------
> > 
> 
> On examination an extra 4 bytes of zeroes had been inserted by LMS
> into the created ADTS audio stream from MPEG-4 file.
> It seems there is padding in the m4a file and so the value of "seek
> offset" to start of audio and length of MPEG4 header are not the same.
> 
> 
> In Movie::findFrameBoundaries - Audio ::Scan is called on initial
> Audio block of m4a stream.
> Data::Dump::dump of variable $info (returned from Audio::Scan) 
> > 
Code:
--------------------
  >   > 
  > [22-01-02 16:38:20.1771] Slim::Formats::Movie::findFrameBoundaries (198)  Dump of info from AudioScan do {
  > require MIME::Base64;
  > {
  > audio_offset      => 22_092,
  > audio_size        => 880_370,
  > avg_bitrate       => 62_768,
  > compatible_brands => ["M4A ", "mp42", "isom", "\0\0\0\0"],
  > dlna_profile      => "AAC_ISO_192",
  > file_size         => 22_116,
  > major_brand       => "mp42",
  > minor_version     => 0,
  > mv_timescale      => 90_000,
  > samplerate        => 22_050,
  > seek_header       => MIME::Base64::decode("
  > .
  > .(deleted)
  > .
  > "),
  > seek_offset       => 22_108,
  > song_length_ms    => 224_351,
  > tracks            => [
  > {
  > audio_object_type => 2,
  > audio_type        => 64,
  > bits_per_sample   => 16,
  > channels          => 1,
  > duration          => 224_351,
  > encoding          => "mp4a",
  > handler_name      => "Sound Media Handler",
  > handler_type      => "soun",
  > id                => 1,
  > max_bitrate       => 37_608,
  > samplerate        => 22_050,
  > },
  > { duration => 224_351, id => 1 },
  > ],
  > };
  > 
  > 
--------------------
> > 
> Audio::Scan - the length of $info->{seek_header} is 22,100
> Audio::Scan - audio_offset is at 22,092 but seek_offset to start of
> audio is 22,108 
> 
> LMS seems to be streaming from end of MPEG4 header when it should be
> streaming from seek_offset which is start of audio. 
> Not sure if the error is in Audio::Scan or Movie.pm.
> 
> I'll try to come up with a solution but any suggestions welcome. I
> need to check Audio::Scan documentation to see if the returned values
> are correct and expected.

The error is probably in movie.pm where I calculate the offset. From
memory, I don’t rely on Audio::Scan when header is at the end of the
file and I need to do an HTTP range to reach it. I assume I made a
mistake and some files have an extended mdat header (or a similar issue)
and I can’t just add 8 to the mdat position.



LMS 8.2 on Odroid-C4 - *SqueezeAMP!*, 5xRadio, 5xBoom, 2xDuet, 1xTouch,
1xSB3. Sonos PLAY:3, PLAY:5, Marantz NR1603, Foobar2000, ShairPortW,
2xChromecast Audio, Chromecast v1 and v2, Squeezelite on Pi,  Yamaha
WX-010, AppleTV 4, Airport Express, GGMM E5, RivaArena 1 & 3
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