I have an MP4 which contains an H264/AVC stream, which contains multiple resolutions.
Below is the output of mediainfo on this file:
General
Complete name : known.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom
File size : 661 KiB
Duration : 15s 960ms
Overall bit rate : 340 Kbps
Writing application : Lavf54.49.102
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : [email protected]
Format settings, CABAC : No
Format settings, ReFrames : 1 frame
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 15s 960ms
Bit rate : 338 Kbps
Width : 176 pixels
Original width : 352 pixels
Height : 144 pixels
Original height : 288 pixels
Display aspect ratio : 1.222
Frame rate mode : Constant
Frame rate : 25.000 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.534
Stream size : 659 KiB (100%)
After some research, the value Lavf54.49.102 appears to indicate that ffmpeg was used to encode this file.
Below is the output of ffplay on this file:
ffplay known.mp4
ffplay version 2.4.3 Copyright (c) 2003-2014 the FFmpeg developers
built on Nov 9 2014 17:21:35 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
configuration: --extra-libs=-ldl --prefix=/opt/ffmpeg --enable-avresample --disable-debug --enable-nonfree --enable-gpl --enable-version3 --enable-x11grab --enable-libpulse --enable-libopencore-amrnb --enable-libopencore-amrwb --disable-decoder=amrnb --disable-decoder=amrwb --enable-libx264 --enable-libx265 --enable-libfdk-aac --enable-libvorbis --enable-libmp3lame --enable-libopus --enable-libvpx --enable-libspeex --enable-libass --enable-avisynth --enable-libsoxr --enable-libxvid
libavutil 54. 7.100 / 54. 7.100
libavcodec 56. 1.100 / 56. 1.100
libavformat 56. 4.101 / 56. 4.101
libavdevice 56. 0.100 / 56. 0.100
libavfilter 5. 1.100 / 5. 1.100
libavresample 2. 1. 0 / 2. 1. 0
libswscale 3. 0.100 / 3. 0.100
libswresample 1. 1.100 / 1. 1.100
libpostproc 53. 0.100 / 53. 0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'known.mp4':= 0B f=0/0
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf54.49.102
Duration: 00:00:15.96, start: 0.000000, bitrate: 339 kb/s
Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 176x144, 338 kb/s, 25 fps, 25 tbr, 1200k tbn, 2400k tbc (default)
Metadata:
handler_name : VideoHandler
[h264 @ 0x7f756800b540] Reinit context to 352x288, pix_fmt: yuv420p
Note the last line [h264 @ 0x7f756800b540] Reinit context to 352x288, pix_fmt: yuv420p; at this point ffplay changes size to match this new resoltuion.
I am currently trying to reproduce this "multiple resolution" effect, firstly on the same video by decoding and then reencoding it, and once that is working I plan to encode another video in the same way to (hopefully) achieve the same. Once that works I shall try to achieve the same with other codecs that support this.
My efforts so far, even reencoding the same video using ffmpeg, have yielded a video where one resolution is simply scaled to be the same size as the other, rather than actually encoding the stream with two different resolutions.
I've tried everything I can think of, ranging from a simple reencode to piping the output of ffmpeg back into ffmpeg, forcing the profile to baseline, converting the stream to mpg, and so on. Nothing appears to be working.
My question is, how can I preserve a resoltuion change within ffmpeg*, rather than it being scaled?
Thank you for any help in advance!
* although if the same result can be achieved with another encoder, that's good too!
