[Ffmpeg-devel] MP3 decoding from RTP stream. Getting "invalid new backstep"

[Martin]

Hi,

>>right before returning:
>>
>>  if (discard_frame) {
>>    //dicard frame is set if an backstep or overread occurs.
>>    for(i=0;i<nb_frames;i++) {
>>      for(ch=0;ch<s->nb_channels;ch++) {
>>        int j;
>>        for(j=0;j<SBLIMIT;j++) {
>>          s->sb_samples[ch][i][j] = 0;
>>        }
>>      }
>>    }
>>  }
>>
>>
>>
>>This didn't worked as expected. Also I found another problem caused by
>>this point in the huffman_decode() function:
>>
>>  if (pos > end_pos2 && last_pos){
>>                /* some encoders generate an incorrect size for this
>>                   part. We must go back into the data */
>>                s_index -= 4;
>>                skip_bits_long(&s->gb, last_pos - pos);
>>                av_log(NULL, AV_LOG_INFO, "overread, skip %d enddists:
>>%d %d\n", last_pos - pos, end_pos-pos, end_pos2-pos);
>>                s->frame_distorted = 1;
>>
>>                break;
>>            }
>>
>>
>>My idea was now to introduce a new flag into the MPADecodeContext:
>>int frame_distorted;
>>
>>Now I set this flag to 0 at the start of decode_frame()
>>and set it to 1 when backstep or overread occurs. At the end of
>>decode_frame() I check the flag and return -1 if it is set. This is
>>working for me. If I send a patch with the new flag, would you include it?
> 
> 
> not without understanding why setting sb_samples to 0 doesnt work
> 
> [...]

It seems to work now, with setting sb_frames to 0. I did it after the
synthesis filter which didn't work. How should I transmit the fact that
a distortion occured in huffmann_decode() to the function
mp_decode_frame()? Can I use the flag for this purpose?
I'm not sure whether I break something if I set sb_samples to 0 directly
at the point where the distortion occurs in huffmann_decode().

Thanks,
Martin