[Cin] Reverse playback hack

[Andrew Randrianasulu]

Hi all!

While testing .prores files I noticed I missed this codec in my hack for faster reverse playback of
I-only video tracks ...

Now I added it there, and on my 4 core AMD reverse playback (2x, 1x) indeed
faster now.

I wonder how much I break shuttle controller higher speeds or complex plugin chains?

Hack attached.

diff --git a/cinelerra-5.1/cinelerra/ffmpeg.C b/cinelerra-5.1/cinelerra/ffmpeg.C
index 70098ca..32867de 100644
--- a/cinelerra-5.1/cinelerra/ffmpeg.C
+++ b/cinelerra-5.1/cinelerra/ffmpeg.C
@@ -1192,10 +1192,19 @@ int FFVideoStream::video_seek(int64_t pos)
        if( pos == curr_pos-1 && !seeked ) return 0;
 // if close enough, just read up to current
        int gop = avctx->gop_size;
-       if( gop < 4 ) gop = 4;
+       if( gop < 4 && gop != 0) gop = 4;
        if( gop > 64 ) gop = 64;
+       if( gop == 0 ) gop = 1;
+       //fprintf(stderr, "GOP: %i \n", gop);
        int read_limit = curr_pos + 3*gop;
        if( pos >= curr_pos && pos <= read_limit ) return 0;
+       // fixup for I-only codecs, not sure why it needed with ffmpeg 4.2
+       if (st->codecpar->codec_id == AV_CODEC_ID_DVVIDEO || st->codecpar->codec_id == AV_CODEC_ID_MJPEG || 
+       st->codecpar->codec_id == AV_CODEC_ID_FFVHUFF || st->codecpar->codec_id == AV_CODEC_ID_DNXHD ||
+       st->codecpar->codec_id ==AV_CODEC_ID_HUFFYUV || st->codecpar->codec_id == AV_CODEC_ID_PRORES) {
+       gop = 1;
+       if( seek(pos - 2*gop, frame_rate) < 0 ) return -1;
+       }
 // guarentee preload more than 2*gop frames
        if( seek(pos - 3*gop, frame_rate) < 0 ) return -1;
        return 1;
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