Decoding MPEG-H without audio scene information (MAE) does not work

[benjamin-weiss]

There are certain MPEG-H files that cannot be decoded properly with Ittiam decoder, libmpegh constantly spouting IA_MPEGH_DEC_INIT_FATAL_INVALID_MCT_ENTRIES error.

Unfortunately we cannot share the files but here is the description of what happens (and hopefully you can reproduce it locally by disabling parsing MAE data):

• the first frame initialises everything properly
• next frame causes internal state reset in impegh_3daudio_config_dec() because of missing audio scene description (by invoking memset(mpeghd_state_struct->ia_audio_specific_config, 0, sizeof(ia_audio_specific_config_struct));) ;
• afterwards most of the data gets re-initialised but MCT part in USAC core decoder does not (it is done in impeghd_mc_init() which is called only in ia_core_coder_dec_process_frame_zero() and not for e.g. second frame);
• so when MCT data in USAC is being decoded, the decoder presumes it has zero channels and refuses to decode non-silent data returning the aforementioned error code;
• because of that decoder is fully reset and re-initialised and the cycle repeats.

We can see two possible solutions for this situation: either omit resetting USAC state in that case, zeroing only selected fields of mpeghd_state_struct->ia_audio_specific_config or re-initialise multichannel information as part of the reset procedure.

[SakethSathuvalli]

Hi @benjamin-weiss, We are working(internally) on some fixes in the MAE handling part. We hope this issue gets addressed with those fixes.

Thanks!