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. Zane _______________________________________________ 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".
