On 4/12/20, Zane van Iperen <z...@zanevaniperen.com> wrote: > On Sat, 11 Apr 2020 22:02:26 +0200 > "Paul B Mahol" <one...@gmail.com> wrote: > >> > >> > Ping. >> > >> > Also, could someone please clarify something for me? >> > >> > When encoding, there's no inherit differences between trellis and >> > non-trellis other then a potentially more-accurate set of nibbles? >> > >> > And the decoder is none the wiser and chews on them both the same >> > way? >> > >> > If I'm right, then this looks to be a decoder issue... >> > >> >> You are wrong, just follow qt adpcm encoder code. >> > > I did. > > > Is it possible, and I don't suggest this lightly, that the trellis code > is bugged, and errors accumulate over time? > > I ask this because all of the encoders (except adpcm_yamaha, which is > different anyway) have either the full sample and/or the step index > periodically written to the bitstream, which is then used to reset the > state machine, thus errors don't accumulate. > > adpcm_ima_ssi doesn't have that, so it relies on the state being > accurate through the entire stream. This would certainly explain the > behaviour I'm seeing in certain cases (see below). > > In both images, the top stream is encoded with '-trellis 0', and the > bottom with '-trellis 1': > - https://0x0.st/iSdS.png > This one's obvious where the problem is. > - https://0x0.st/iSdQ.png > This is more subtle, but the entire stream is offset slightly. It's > more noticeable at the start and end. > > > For reference, here's the code I'm using. You'll see it's basically > the same as the adpcm_ima_qt code: > > if (avctx->trellis > 0) { > FF_ALLOC_OR_GOTO(avctx, buf, n * avctx->channels, error); > > for (ch = 0; ch < avctx->channels; ch++) { > adpcm_compress_trellis(avctx, samples + ch, buf + n * ch, > c->status + ch, n, avctx->channels); > c->status[ch].prev_sample = c->status[ch].predictor; > } > > for (i = 0; i < n; i++) { > for (ch = 0; ch < avctx->channels; ch++) { > put_bits(&pb, 4, buf[n * ch + i]); > } > } > av_free(buf); > } > > > Or maybe I just don't fully understand how trellis works.
Yes. that is 100% correct. Also you ignored fact that you do not update nodes for SSI variant in compress trellis. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
