[FFmpeg-trac] #1407(avcodec:new): aac: 960/120 MDCT window is not implemented

FFmpeg trac at avcodec.org
Tue Jul 4 22:46:34 EEST 2017

#1407: aac: 960/120 MDCT window is not implemented
             Reporter:  cehoyos      |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  wish         |                Component:  avcodec
              Version:  git-master   |               Resolution:
             Keywords:  aac          |               Blocked By:
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  0            |

Comment (by Basic.Master):

 All that DABMON streams are still AAC with 960 samples/frame. The problem
 is that these streams use the ADTS format, which cannot incorporate the
 signalling whether 960 or 1024 was used. But this signalling is required,
 as all AAC decoders (I have seen so far) otherwise default to 1024
 samples/frame and the audio sounds slow and low-pitched, as described!

 The 960/1024 samples/frame signalling is done by the `frameLengthFlag`
 within the `GASpecificConfig`, which in turn is contained in the
 `AudioSpecificConfig` (all defined in ISO 14496-3). So for correct
 playback, such AAC content has to be stored in a format that contains this
 config. This may be e.g. just an MP4/ISOBMFF container or an LATM stream.

 `ODR-AudioEnc` does not produce plain AAC frames, but the so-called
 Superframes. A Superframe is a special container defined by DAB+ (ETSI TS
 102 563) that has a fixed length (for a given service). Within a
 Superframe, there are (depending on the usage of SBR, and of 48/32 kHz) 2
 to 6 AAC frames of variable length. As this format is intended for DAB+
 transmission, it is hardly surprising that it cannot be played without
 modification by usual players.

 I will provide DAB+ samples in both LATM and MP4 format, with the
 necessary 960 signalling. Both are played correctly by VLC, but fail with
 `ffplay` and the mentioned error message.

Ticket URL: <https://trac.ffmpeg.org/ticket/1407#comment:21>
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