# Resizing video with ffmpeg ## Intro I've recorded a video on a MacBook Pro 2019, 16'' in QuickTime player. It's about 100 Mb. I wanted to convert it to something smaller without losing much quality. ## TLDR Use this: ``` ffmpeg -i input.mov -vcodec libx264 -crf 28 -f mov -acodec copy output.mov ``` CRF parameter - *constant rate factor* - defines the quality (the lower the number, the better quality), it can take values from 0 to 53. For x264, sane values are between 18 and 28. Above I use 28, which is the lowest quality, which is still kinda acceptable. ## Details First I've looked at this answer: Which gives some command line using `ffmpeg`. I've installed ffmpeg (`brew install ffmpeg`) and became interested in what codecs/containers it supports and what all this stuff generally means. Also, by following advice from the article above I could convert my file easily from 100 Mb to 9 Mb using this command line: ``` ffmpeg -i input.mov -vcodec libx265 -crf 28 output.mp4 ``` However, when I tried to send it via WhatsApp, it was sent fine (although I need to send it as a document, it's not recoginised when I try to send it as audio/video, i.e. the file is just not visible, so I can't select it as a video), but when I tried to open it on iPhone SE, it didn't work. So ok, I googled a little bit: iPhones should be opening .mp4 containers without any issues, so I was not sure why it didn't work. Eventually it turned out that the problem was with H.265 codec (which is more efficient, but less supported), in fact for better support one should use more popular H.264 codec which is supported well on iPhones (and presumably other devices). If I encode my files like this: ``` ffmpeg -i input.mov -vcodec libx264 -crf 28 -f mov output.mov ``` It works fine, on macOS I can immediately see preview of the video, I can send it as a video in WhatsApp and it's played normally on iPhone. Also, if you want to keep the sound as is, there is `-c:a copy` option (which means "codec:audio = copy": ``` ffmpeg -i input.mov -vcodec libx264 -crf 28 -f mov -acodec copy output.mov ``` ## Useful command for inspecting files information ``` ffprobe -show_streams ``` ## Links -- ffmpeg doc -- a nice description of CRF parameter with plots -- containers and codecs big table --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://notes.iveselov.info/audio-video-encoding-tips/resizing-video-with-ffmpeg.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.