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

[Michael Niedermayer]

Hi

On Fri, Nov 03, 2006 at 12:25:30PM +0100, Martin wrote:
> 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().

huffmann_decode() should return -1 if theres an error

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or copy any book
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