A video file need to be transferred for further video processing. Sharing raw video (y4m) seems impossible. I am having two options
Encoding video file to h264 with crf 0 - lossless - file size is huge.
Encoding video file to h264 with crf 17/18 - virtually lossless - file size is manageable.
After the video is shared, it will be re-encoded only once with crf 22/23 with client info added.
Option 2 seems okay, but the quality should not be degraded on the re-encoding.
Is going with Option 1 and managing huge file is better option than Option 2?
Related
I am using ffmpeg on Linux to transcode video files. The files are video from a race car camera. They have been downloaded from Youtube as "webm" format. I want to compare two of the videos, side-by-side, using GridPlayer, which uses vlc as its underlying video processor. GridPlayer has very nice, frame-by-frame controls, but, they are very slow. What video codec should I use to impose the least decoding overhead on vlc/GridPlayer for smoother playback?
I have tried re-encoding as h264, 1920x1080, 30 fps, in mp4 container. I have since discovered a "-tune fastdecode" option that seems to be helpful, along with resizing to 854x480. Any other suggestions?
I am wondering when I convert a .mp4 to .mkv using the following command if the quality changes.
ffmpeg -i in.mp4 out.mkv
The input file, in.mp4 has a file size of 297 megabytes, while the out.mkv file has a size of 249 megabytes, ~15% lower. Upon manual inspection, the resolution, video, and audio streams are the same before/after (as I would have expected given my (limited) knowledge of ffmpeg).
Is the 15% size decrease by simply converting to mkv actually not affect the quality of the video? If so this seems like a very reasonable way of freeing up some space on my computer.
The quality gets worse
This is due to generation loss because you are re-encoding the video and audio to lossy formats. But you may not notice the difference.
The output file size will vary depending on the input format, if it was encoded well or badly, your output format, and the settings you use.
MP4 to MKV without quality loss
You can just re-mux and avoid re-encoding by using stream copy mode:
ffmpeg -i input.mp4 -c copy output.mkv
You can think of it like a copy and paste. The video and audio is untouched and just put into a new container.
I am using ffmpeg to rotate videos 90 or 180 degrees in a Python script. It works great. But, I am curious as to why the output file would be a smaller amount of bytes than the input file.
Here are the commands I use:
180 degrees:
ffmpeg -i ./input.mp4 -preset veryslow -vf "transpose=2,transpose=2,format=yuv420p" -metadata:s:v rotate=0 -codec:v libx264 -codec:a copy ./output.mp4
90 degrees:
ffmpeg -i ./input.mp4 -vf "transpose=2" ./output.mp4
For example, a GoPro Hero 3 MP4 file was originally 2.0 GB. The resulting output file was 480.9 MB. Another GoPro file was 2.0 and its resulting file was 671.5 MB. Is this maybe because the GoPro files were 2.0 but contains empty space, sort of like how some NTFS filesystems make a minimal 4k file, even when there is less bytes in it?
If this isn't the GoPro Hero 3, how do I rotate the files 90 or 180 degrees but ensure the output file size is the same? Or, is data loss expected? Does the data loss have to do with the format?
Note that the quality of the video doesn't appear to be damaged, which is good. So, I am interested in learning more about why this is happening, then I can read the section of ffmpeg documentation that is relevant to this.
Thank you!
Bitrate is ignored from the start
ffmpeg fully decodes the input into uncompressed raw video and audio (except when stream copying – more about that below). The input format or bitrate does not matter: it does this for all formats. The encoder then works from these raw, decoded frames. See diagram.
H.264 vs H.264
Your input and output are both H.264. A format, such as H.264, is created by an encoder. Anyone can make an encoder. However, not all encoders are equal. Given the same input, the output from one H.264 encoder may have the same quality as an output from another H.264 encoder, but the bitrate may be several times smaller.
The GoPro H.264 encoder was made to work on a platform with limited hardware. That means bitrate (file size) is sacrificed for speed and quality. x264 is the ultimate H.264 encoder: nothing can beat its quality-to-bitrate ratio.
Rotate without re-encoding
You can stream copy (re-mux) and rotate at the same time. The rotation is handled by the metadata/sidedata:
ffmpeg -i input.mp4 -metadata:s:v rotate=90 -c copy output.mp4
Downside is your player/device may ignore the rotation, so you may have to physically rotate with filters which requires re-encoding, and therefore stream copy can't be used.
I had the same rotation issue once...
I fixed it by "resetting" the rotation instead...
ffmpeg ...... -metadata:s:v rotate="0" ......
I am new to video encoding and trying to encode a music video for the apple itunes video store.
I am currently using FFmpeg for encoding.
My source file is mp4 file type and file size=650MB
I encode the file using the Apple ProRes 422 (HQ) codec and output a mov file.
ffmpeg -y -i busy1.mp4 -vcodec prores -profile:v 3 -r "29.97" -c:a mp2 busy2.mov
I am trying to encode the video according to the following specs:
● Apple ProRes 422 (HQ)
● VBR expected at ~220 Mbps
Encoded PASP Converted to ProRes From
1920 x 1080 1:1 HDCAM SR, D5, ATSC
1280 x 720 1:1 ATSC progressive
29.97 interlaced frames per second for video sourced
Music Video Audio Source Profile
● MPEG-2 layer II stereo
● 384 kpbs
● 48Khz
The file is encoded perfectly fine however the output is 6Gb in size.
Why would the file be so large after encoding?
Am I doing something wrong here?
The Apple ProRes is not intended for high compression. It is an intermediate codec used in post-production which optimizes the storage as opposed to keeping the videos uncompressed while retaining a high image quality.
You are supposed to use your uncompressed source file as input to retain the maximum quality and not an already lossy-compressed video.
You only mentioned the container format of your input file: MP4 but not the codecs which is the actual important information.
Since the HQ flavor of ProRes uses 220 Mbps the file size can actually increase but you don't gain anything in quality if the source is lossy.
See more here: Apple ProRes
Though you don't gain much by decompressing a source clip thats "Lossy", you do gain in some ways. Compressed video uses a compressed color palette, which can be detrimental when making color corrections or corrections to detail level, especially when you're given interlaced footage to clean up. If you put in the time on detail, microcontrast, and color, you know the benefit of expanded color detail for compressing back down. It also encodes much faster on the back end of your edits. Simply compressing the data down is faster than expanding and then compressing.
However, if you recompress all your video down to the same size and codec as what went in, most encoders and editor apps now test the datarate of the GOP, working on only those GOP's that need to be redone to fit the new settings.
I don't know much about multimedia knowledge. I know sony .mts file is a type of H.264 container. I use ffmpeg to dump my .mts file into a .mpeg file. Except the .mpeg file is shrunk around 5 times smaller in size than .mts, the ffmpeg dump information on both files is identical. I am confusing why .mts files have large size. What important features are lost by my conversion?
Thanks!
Kejia
Thanks to all answers.
I checked the output of both again and found that there is one different place: bitrate. Then I definitely lost quality. Now I adjust the bit rate in terms of the expectation to displaying equipment---yes, considering displaying equipments is necessary (an expert's advice): $ ffmpeg -b 9498k -i my.mts my.mpg. Another interesting option is -ab, audio bit rate.
MTS files typically come from high-definition camcorders. They use the AVCHD coded which uses MPEG-4 AVC/H.264 video encoding and Dolby AC-3 (Dolby Digital) or uncompressed linear PCM audio coding. Are you sure that you are not decreasing the quality or resolution?
Your file has H.264/MPEG-4 AVC video compression and Dolby Digital (AC-3) audio compression or uncompressed LPCM audio, so this equals to a fairly large source file size.
When you export (convert) to MPG, you most likely perform a lossy compression. Please double check, especially the audio track.