Hi, The second pass shows error (IO error: Error number 0 occurred) but the file gets generated and looks fine, but I don't know whether it actually used the 1st pass. C:\Users\ramprasad>ffmpeg.exe -i foreman_qcif.y4m -b:v 128k -pass 1 -vcodec h263 -f 3gp -y NUL ffmpeg version N-69422-gf5722ba Copyright (c) 2000-2015 the FFmpeg developers built on Jan 30 2015 22:02:24 with gcc 4.9.2 (GCC) configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib libavutil 54. 18.100 / 54. 18.100 libavcodec 56. 21.101 / 56. 21.101 libavformat 56. 19.100 / 56. 19.100 libavdevice 56. 4.100 / 56. 4.100 libavfilter 5. 9.102 / 5. 9.102 libswscale 3. 1.101 / 3. 1.101 libswresample 1. 1.100 / 1. 1.100 libpostproc 53. 3.100 / 53. 3.100 Input #0, yuv4mpegpipe, from 'foreman_qcif.y4m': Duration: N/A, bitrate: N/A Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 176x144, 25 fps, 25 tbr, 25 tbn, 25 tbc Output #0, 3gp, to 'NUL': Metadata: encoder : Lavf56.19.100 Stream #0:0: Video: h263 (s263 / 0x33363273), yuv420p, 176x144, q=2-31, pass 1, 128 kb/s, 25 fps, 12800 tbn, 25 tbc Metadata: encoder : Lavc56.21.101 h263 Stream mapping: Stream #0:0 -> #0:0 (rawvideo (native) -> h263 (native)) Press [q] to stop, [?] for help frame= 300 fps=0.0 q=8.6 Lsize= 276kB time=00:00:12.00 bitrate= 188.5kbits/s video:274kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.707967% C:\Users\ramprasad>ffmpeg.exe -i foreman_qcif.y4m -b:v 128k -pass 2 -vcodec h263 -f 3gp -y test.3gp ffmpeg version N-69422-gf5722ba Copyright (c) 2000-2015 the FFmpeg developers built on Jan 30 2015 22:02:24 with gcc 4.9.2 (GCC) configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib libavutil 54. 18.100 / 54. 18.100 libavcodec 56. 21.101 / 56. 21.101 libavformat 56. 19.100 / 56. 19.100 libavdevice 56. 4.100 / 56. 4.100 libavfilter 5. 9.102 / 5. 9.102 libswscale 3. 1.101 / 3. 1.101 libswresample 1. 1.100 / 1. 1.100 libpostproc 53. 3.100 / 53. 3.100 Input #0, yuv4mpegpipe, from 'foreman_qcif.y4m': Duration: N/A, bitrate: N/A Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 176x144, 25 fps, 25 tbr, 25 tbn, 25 tbc IO error: Error number 0 occurred Output #0, 3gp, to 'test.3gp': Metadata: encoder : Lavf56.19.100 Stream #0:0: Video: h263 (s263 / 0x33363273), yuv420p, 176x144, q=2-31, pass 2, 128 kb/s, 25 fps, 12800 tbn, 25 tbc Metadata: encoder : Lavc56.21.101 h263 Stream mapping: Stream #0:0 -> #0:0 (rawvideo (native) -> h263 (native)) Press [q] to stop, [?] for help frame= 300 fps=0.0 q=9.0 Lsize= 169kB time=00:00:12.00 bitrate= 115.7kbits/s video:167kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.159217% Also, For the same command line, an older version of ffmpeg (dec-2013) fails in the second pass with the error [h263 @ 0192FBC0] statistics are damaged at line 0, parser out=0 Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height Does h263 (in ffmpeg) support 2 pass encoding? Thanks