Re: [FFmpeg-user] Basic Video Manipulation Qustions
Le 27/10/2022 à 17:46, John Van Ostrand a écrit : Hi All, The RAW video discussion had me thinking about resolution and bit rates for video and I had some questions. These are not how-to questions but general video questions. I'm an amateur so the contest of these questions is around video for home movies and social media, stored and shared as data files, and displayed on computers, tablets, and TVs. 1. Why does it make sense to convert from a lossy format to raw? You're not gaining any more detail. It can make sense for processing purpose 2. Does re-rendering video over and over at the same resolution, frame rate, and bit rate cause degradation? For example, if I want to make several changes to the video, like colour correction, splicing out sections, transitions, titling, etc. should I be trying to do that all in one command? decompressing/recompressing with the exact same codec and exact same encoding parameters, and without making any change on the video, should not cause significant degradations. In all others cases degradations are possible. 3. I understand that -c copy is a great way to eliminate time and preserve detail but what's the best way to do this when converting from one codec to another, or when performing editing or other changes? If the source had been encoded with a very high quality (say "transparent", or nearly), then you can consider if was like uncompressed. Then you can choose whatever quality you want on output. Otherwise, if you want to maintain quality as far as possible, it's better to choose a slightly higher output quality than the one of the source video. 4. How important is it to keep standard resolutions, frame rates, and bit rates? Do hardware decoders do better with those? Do software decoders handle weird resolutions better? Will strange decoding artifacts appear more often with non-standard parameters? This is a much too general question... Some mobile and low power devices have restrictions, but rather linked to the power needed to decode the streams. ___ 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".
Re: [FFmpeg-user] Basic Video Manipulation Qustions
I suppose there's a couple of other things to be said about raw video, or in fact any less-complex codec. First, it requires less CPU time to play it back. If for some reason you're storage-rich but CPU poor in some very specific application, especially some piece of embedded electronics where you're playing back a fairly low-resolution animated icon, or some short loop of video, then it may be worthwhile allocating more storage for something in order to have it play back quickly with low effort. Low effort can mean low cost hardware, low power consumption, and so on. Storage is generally more expensive than CPU time, but depending on the specifics of certain projects may not always be. Second, and leading on from that, including a codec can involve a lot more complexity in some piece of software or firmware. Using someone else's API to decode a bit of video can involve a lot of extremely expensive software engineering time, as well as engaging licensing issues that you may not want to deal with. This is why things like raw video, as well as old, outdated codecs, still get used. P ___ 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".
Re: [FFmpeg-user] Basic Video Manipulation Qustions
Carl's comments are great. I try to carve out duplicate content, but this Q format may allow for leaving Carl's initial reply inline. >> 1. Why does it make sense to convert from a lossy format to raw? >> You're not >> gaining any more detail. > > It doesn't, unless you need raw for some further processing (that's > what happens in the ffmpeg pipeline- demux, decode, filter/transform, > encode, mux, see https://ffmpeg.org/ffmpeg.html#Detailed-description). > >> 2. Does re-rendering video over and over at the same resolution, frame >> rate, and bit rate cause degradation? For example, if I want to make >> several changes to the video, like colour correction, splicing out >> sections, transitions, titling, etc. should I be trying to do that >> all in >> one command? > > It can, and yes or store the intermediate files in a lossless format > (which could be raw frames in a container); I prefer intermediate > files as the command lines can get complex and if I mess something up > or don't like it, part of the work has already been done (as an > ancient IT person, keeping backups of each step is assumed). > > Or use some ffmpeg library based software that allows for you to > effectively script/render the output. The stacked command-line ability of ffmpeg is a blessing and a curse; python-ffmpeg (and other) wrappers really help to harness the complexity. There are several python wrapper efforts, here are two of the most popular: https://github.com/PyAV-Org/PyAV and https://github.com/kkroening/ffmpeg-python (doing a search on github illuminates 850 repos) >> 3. I understand that -c copy is a great way to eliminate time and >> preserve >> detail but what's the best way to do this when converting from one >> codec to >> another, or when performing editing or other changes? > > Copy does just that, it copies; changing the > encoding/size/pixel-format/etc requires going through an > uncompressed/raw state (the pipeline). We use Copy to preserve quality between various ffmpeg actions when possible. > >> 4. How important is it to keep standard resolutions, frame rates, and >> bit >> rates? Do hardware decoders do better with those? Do software decoders >> handle weird resolutions better? Will strange decoding artifacts appear >> more often with non-standard parameters? > > Importance is relative. If the final output must be played on a wide > varieties of player, then stick to the standards and it's more likely > to work. Bit rates- AFAIK there are no "standards" for compressed > video & audio, only conventions or guidelines to use a certain max > rate to get a given quality (and some media, like dvd/bluray, can only > go so fast). I can't answer for how s/w decoders play with > non-standard resolutions. And as I understand, some decoders get wonky > the resolution isn't divisible by 8. HLS (http packaged mp4) has some Apple recommended bitrates and sizes. For example, they recommend 2mbps avg-bitrate for wifi streaming and 730kbps for cellular streaming along with a slew of pixel recommendations (https://developer.apple.com/documentation/http_live_streaming/http_live_streaming_hls_authoring_specification_for_apple_devices). ___ 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".
Re: [FFmpeg-user] Basic Video Manipulation Qustions
[knocking off a quick answer] On 10/27/2022 8:46 AM, John Van Ostrand wrote: 1. Why does it make sense to convert from a lossy format to raw? You're not gaining any more detail. It doesn't, unless you need raw for some further processing (that's what happens in the ffmpeg pipeline- demux, decode, filter/transform, encode, mux, see https://ffmpeg.org/ffmpeg.html#Detailed-description). 2. Does re-rendering video over and over at the same resolution, frame rate, and bit rate cause degradation? For example, if I want to make several changes to the video, like colour correction, splicing out sections, transitions, titling, etc. should I be trying to do that all in one command? It can, and yes or store the intermediate files in a lossless format (which could be raw frames in a container); I prefer intermediate files as the command lines can get complex and if I mess something up or don't like it, part of the work has already been done (as an ancient IT person, keeping backups of each step is assumed). Or use some ffmpeg library based software that allows for you to effectively script/render the output. 3. I understand that -c copy is a great way to eliminate time and preserve detail but what's the best way to do this when converting from one codec to another, or when performing editing or other changes? Copy does just that, it copies; changing the encoding/size/pixel-format/etc requires going through an uncompressed/raw state (the pipeline). 4. How important is it to keep standard resolutions, frame rates, and bit rates? Do hardware decoders do better with those? Do software decoders handle weird resolutions better? Will strange decoding artifacts appear more often with non-standard parameters? Importance is relative. If the final output must be played on a wide varieties of player, then stick to the standards and it's more likely to work. Bit rates- AFAIK there are no "standards" for compressed video & audio, only conventions or guidelines to use a certain max rate to get a given quality (and some media, like dvd/bluray, can only go so fast). I can't answer for how s/w decoders play with non-standard resolutions. And as I understand, some decoders get wonky the resolution isn't divisible by 8. Hope that helps, it's a bit shy on technical rigor. Later, z! ___ 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".
[FFmpeg-user] Basic Video Manipulation Qustions
Hi All, The RAW video discussion had me thinking about resolution and bit rates for video and I had some questions. These are not how-to questions but general video questions. I'm an amateur so the contest of these questions is around video for home movies and social media, stored and shared as data files, and displayed on computers, tablets, and TVs. 1. Why does it make sense to convert from a lossy format to raw? You're not gaining any more detail. 2. Does re-rendering video over and over at the same resolution, frame rate, and bit rate cause degradation? For example, if I want to make several changes to the video, like colour correction, splicing out sections, transitions, titling, etc. should I be trying to do that all in one command? 3. I understand that -c copy is a great way to eliminate time and preserve detail but what's the best way to do this when converting from one codec to another, or when performing editing or other changes? 4. How important is it to keep standard resolutions, frame rates, and bit rates? Do hardware decoders do better with those? Do software decoders handle weird resolutions better? Will strange decoding artifacts appear more often with non-standard parameters? Thanks -- John Van Ostrand At large on sabbatical ___ 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".
