On 5/20/25 10:32 PM, Def Etienne wrote: >> On 19 May 2025, at 03:01, George Welch via ffmpeg-user >> <ffmpeg-user@ffmpeg.org> wrote: >> >> Howdy ffmpeg users. >> >> I have found a behavior that seems strange to me. The following two >> commands: >> >> $ ffmpeg -i input.mkv -an -c:v libx265 -preset slow -crf 21 output1.mkv >> >> and >> >> $ ffmpeg -i input.mkv -an -c:v libx265 -preset slow -crf 21 -vf >> "setpts=PTS-STARTPTS" output2.mkv >> >> produce output files that are very different. The input file is 1080p h264 >> recorded at 15Mbps. The output file in the first case is about 1.66 times >> larger than the second output file. The video channel in the first case >> averages 7342 kbps while the video channel in the second case averages 4423 >> kbps. >> >> Unsurprisingly, dumping frames to png files and using imagemagick to compare >> them shows that the first output file has much higher fidelity to the >> original than the second. >> >> This is with ffmpeg 7.1.1 installed via homebrew on a fairly modern macbook >> pro. Checking on a linux machine with a fairly old intel xeon processor >> (all I have access to) also with ffmpeg installed via homebrew produces >> nearly identical files. >> >> I wonder if this a bug in the mac version of ffmpeg? I don't see why the >> setpts filter should produce a much lower bitrate, nor why it would be >> different under linux. > The complete uncut console output in each case would have been a good > starting point to explain the differences. > > Def
Happy to! For the first case, with no filter: george@austin:test2$ ffmpeg -i input.mkv -an -c:v libx265 -preset slow -crf 21 output1.mkv ffmpeg version 7.1.1 Copyright (c) 2000-2025 the FFmpeg developers built with Apple clang version 15.0.0 (clang-1500.3.9.4) configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1.1-with-options_1 --enable-shared --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-libaom --enable-libdav1d --enable-libharfbuzz --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-demuxer=dash --enable-neon --enable-opencl --enable-audiotoolbox --enable-videotoolbox --disable-htmlpages --enable-libfdk-aac --enable-nonfree libavutil 59. 39.100 / 59. 39.100 libavcodec 61. 19.101 / 61. 19.101 libavformat 61. 7.100 / 61. 7.100 libavdevice 61. 3.100 / 61. 3.100 libavfilter 10. 4.100 / 10. 4.100 libswscale 8. 3.100 / 8. 3.100 libswresample 5. 3.100 / 5. 3.100 libpostproc 58. 3.100 / 58. 3.100 Input #0, matroska,webm, from 'input.mkv': Metadata: ENCODER : Lavf61.1.100 Duration: 00:00:10.00, start: 0.000000, bitrate: 15814 kb/s Stream #0:0: Video: h264 (Main), yuv420p(tv, bt709, progressive), 1920x1080, 30 fps, 30 tbr, 1k tbn Metadata: DURATION : 00:00:10.000000000 Stream #0:1: Audio: flac, 48000 Hz, stereo, s16 Metadata: title : Track1 DURATION : 00:00:09.984000000 Stream mapping: Stream #0:0 -> #0:0 (h264 (native) -> hevc (libx265)) Press [q] to stop, [?] for help x265 [info]: HEVC encoder version 4.1+1-1d117be x265 [info]: build info [Mac OS X][clang 16.0.0][64 bit] 8bit+10bit+12bit x265 [info]: using cpu capabilities: NEON Neon_DotProd Neon_I8MM x265 [info]: Main profile, Level-4 (Main tier) x265 [info]: Thread pool created using 12 threads x265 [info]: Slices : 1 x265 [info]: frame threads / pool features : 3 / wpp(17 rows) x265 [info]: Coding QT: max CU size, min CU size : 64 / 8 x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra x265 [info]: ME / range / subpel / merge : star / 57 / 3 / 3 x265 [info]: Keyframe min / max / scenecut / bias : 25 / 250 / 40 / 5.00 x265 [info]: Lookahead / bframes / badapt : 25 / 4 / 2 x265 [info]: b-pyramid / weightp / weightb : 1 / 1 / 0 x265 [info]: References / ref-limit cu / depth : 4 / on / on x265 [info]: AQ: mode / str / qg-size / cu-tree : 2 / 1.0 / 32 / 1 x265 [info]: Rate Control / qCompress : CRF-21.0 / 0.60 x265 [info]: tools: rect limit-modes rd=4 psy-rd=2.00 rdoq=2 psy-rdoq=1.00 x265 [info]: tools: rskip mode=1 signhide tmvp strong-intra-smoothing lslices=4 x265 [info]: tools: deblock sao Output #0, matroska, to 'output1.mkv': Metadata: encoder : Lavf61.7.100 Stream #0:0: Video: hevc, yuv420p(tv, bt709, progressive), 1920x1080, q=2-31, 30 fps, 1k tbn Metadata: DURATION : 00:00:10.000000000 encoder : Lavc61.19.101 libx265 Side data: cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A [out#0/matroska @ 0x600001d40000] video:8958KiB audio:0KiB subtitle:0KiB other streams:0KiB global headers:2KiB muxing overhead: 0.058398% frame= 300 fps= 17 q=29.2 Lsize= 8963KiB time=00:00:09.93 bitrate=7392.2kbits/s speed=0.562x x265 [info]: frame I: 2, Avg QP:20.59 kb/s: 44433.72 x265 [info]: frame P: 70, Avg QP:22.11 kb/s: 20672.38 x265 [info]: frame B: 228, Avg QP:28.77 kb/s: 2918.24 x265 [info]: Weighted P-Frames: Y:2.9% UV:2.9% encoded 300 frames in 17.65s (17.00 fps), 7337.64 kb/s, Avg QP:27.16 For the second case, with the setpts filter: george@austin:test2$ ffmpeg -i input.mkv -an -c:v libx265 -preset slow -crf 21 -vf "setpts=PTS-STARTPTS" output2.mkv ffmpeg version 7.1.1 Copyright (c) 2000-2025 the FFmpeg developers built with Apple clang version 15.0.0 (clang-1500.3.9.4) configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1.1-with-options_1 --enable-shared --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-libaom --enable-libdav1d --enable-libharfbuzz --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-demuxer=dash --enable-neon --enable-opencl --enable-audiotoolbox --enable-videotoolbox --disable-htmlpages --enable-libfdk-aac --enable-nonfree libavutil 59. 39.100 / 59. 39.100 libavcodec 61. 19.101 / 61. 19.101 libavformat 61. 7.100 / 61. 7.100 libavdevice 61. 3.100 / 61. 3.100 libavfilter 10. 4.100 / 10. 4.100 libswscale 8. 3.100 / 8. 3.100 libswresample 5. 3.100 / 5. 3.100 libpostproc 58. 3.100 / 58. 3.100 Input #0, matroska,webm, from 'input.mkv': Metadata: ENCODER : Lavf61.1.100 Duration: 00:00:10.00, start: 0.000000, bitrate: 15814 kb/s Stream #0:0: Video: h264 (Main), yuv420p(tv, bt709, progressive), 1920x1080, 30 fps, 30 tbr, 1k tbn Metadata: DURATION : 00:00:10.000000000 Stream #0:1: Audio: flac, 48000 Hz, stereo, s16 Metadata: title : Track1 DURATION : 00:00:09.984000000 Stream mapping: Stream #0:0 -> #0:0 (h264 (native) -> hevc (libx265)) Press [q] to stop, [?] for help x265 [info]: HEVC encoder version 4.1+1-1d117be x265 [info]: build info [Mac OS X][clang 16.0.0][64 bit] 8bit+10bit+12bit x265 [info]: using cpu capabilities: NEON Neon_DotProd Neon_I8MM x265 [info]: Main profile, Level-6.1 (Main tier) x265 [info]: Thread pool created using 12 threads x265 [info]: Slices : 1 x265 [info]: frame threads / pool features : 3 / wpp(17 rows) x265 [info]: Coding QT: max CU size, min CU size : 64 / 8 x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra x265 [info]: ME / range / subpel / merge : star / 57 / 3 / 3 x265 [info]: Keyframe min / max / scenecut / bias : 25 / 250 / 40 / 5.00 x265 [info]: Lookahead / bframes / badapt : 25 / 4 / 2 x265 [info]: b-pyramid / weightp / weightb : 1 / 1 / 0 x265 [info]: References / ref-limit cu / depth : 4 / on / on x265 [info]: AQ: mode / str / qg-size / cu-tree : 2 / 1.0 / 32 / 1 x265 [info]: Rate Control / qCompress : CRF-21.0 / 0.60 x265 [info]: tools: rect limit-modes rd=4 psy-rd=2.00 rdoq=2 psy-rdoq=1.00 x265 [info]: tools: rskip mode=1 signhide tmvp strong-intra-smoothing lslices=4 x265 [info]: tools: deblock sao Output #0, matroska, to 'output2.mkv': Metadata: encoder : Lavf61.7.100 Stream #0:0: Video: hevc, yuv420p(tv, bt709, progressive), 1920x1080, q=2-31, 1k tbn Metadata: DURATION : 00:00:10.000000000 encoder : Lavc61.19.101 libx265 Side data: cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A [out#0/matroska @ 0x60000095c540] video:5377KiB audio:0KiB subtitle:0KiB other streams:0KiB global headers:2KiB muxing overhead: 0.096275% frame= 300 fps= 19 q=33.8 Lsize= 5382KiB time=00:00:09.90 bitrate=4453.7kbits/s speed=0.643x x265 [info]: frame I: 2, Avg QP:24.75 kb/s: 1110316.00 x265 [info]: frame P: 70, Avg QP:26.52 kb/s: 405911.66 x265 [info]: frame B: 228, Avg QP:32.98 kb/s: 58793.19 x265 [info]: Weighted P-Frames: Y:2.9% UV:2.9% encoded 300 frames in 15.36s (19.53 fps), 146797.66 kb/s, Avg QP:31.42 I can also post the input and output files on my cloud server if you want to try them. However, I have tried several different input files and it does not seem to matter. Thanks again, --George _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
