I want to make an app, that will have an feature of recording in a loop. That means, app will continuously record video and when a user hits "end of recording" button, the video will have only the last 1 minute recorded. What is the best way to achieve this?
As far as I know, there is no simple way to achieve this. Some rough ideas, though, in order of increasing difficulty:
If you can safely assume that the total recording time will be fairly short (i.e., you won't run out of storage space on the device), you could record the entire video and then perform a post-processing step that trims the video to size.
Record the video in one-minute chunks. When the user stops recording, compute how much of the previous chunk you need to prepend to the current chunk. Stitch the chunks together.
Register as a PreviewCallback and store the video frames in your own file format. Periodically remove the frames that you don't care about because they're too old. You would need to store the audio separately, and then you would need to transcode the custom format into a standard format.
Each of these would probably require some NDK code to do the work efficiently.
Related
My android app plays videos in Exoplayer 2, and now I'd like to play a video backwards.
I searched around a lot and found only the idea to convert it to a gif and this from WeiChungChang.
Is there any more straight-forward solution? Another player or a library that implements this for me is probably too much to ask, but converting it to a reverse gif gave me a lot of memory problems and I don't know what to do with the WeiChungChang idea. Playing only mp4 in reverse would be enough tho.
Videos are frequently encoded such that the encoding for a given frame is dependent on one or more frames before it, and also sometimes dependent on one or more frames after it also.
In other words to create the frame correctly you may need to refer to one or more previous and one or more subsequent frames.
This allows a video encoder reduce file or transmission size by encoding fully the information for every reference frame, sometimes called I frames, but for the frames before and/or after the reference frames only storing the delta to the reference frames.
Playing a video backwards is not a common player function and the player would typically have to decode the video as usual (i.e. forwards) to get the frames and then play them in the reverse order.
You could extend ExoPlayer to do this yourself but it may be easier to manipulate the video on the server side if possible first - there exist tools which will reverse a video and then your players will be able to play it as normal, for example https://www.videoreverser.com, https://www.kapwing.com/tools/reverse-video etc
If you need to reverse it on the device for your use case, then you could use ffmpeg on the device to achieve this - see an example ffmpeg command to do this here:
https://video.stackexchange.com/a/17739
If you are using ffmpeg it is generally easiest to use via a wrapper on Android such as this one, which will also allow you test the command before you add it to your app:
https://github.com/WritingMinds/ffmpeg-android-java
Note that video manipulation is time and processor hungry so this may be slow and consume more battery than you want on your mobile device if the video is long.
I am Writing video player in android. So far i could able to capture the frames, with the help of av_read_frame and avcodec_decode_video2, and updating to SDL2.0. I have followed dranger tutorial02.c http://dranger.com/ffmpeg/ .
Sudo Code is :
while (1)
{
1. Read packet
2. check if video frame; if not Go to Step 3.
2.1 if video frame, then update with SDL_UpdateYUVTexture,
3. Handle SDL Event
4. Clear the Renderer.
5. Present Renderer.
}
I wonder, do i need to take care of synchronization of video, dts/pts calculation while i need only to display video?
This scenario works well in the samsung, but not in other mobiles.
What woud be your advice?
It depends. If you're ok with the fact that your video will a) play as fast as the device can decode it and b) will play with different speed on different devices and even on the same device depending on other processes, then you don't need to synchronize, and can just dump the frames as soon as they're decoded.
Otherwise you still need to synchronize the video output to PTS. Since you don't have audio, and won't have audio clock, your only option would be to synchronize the video to the system clocks which makes it simpler.
I'm working on an android app that plays video (using video view). the video is meant to have both music (left and right) and narration, but I want to selectively be able to turn off the narration track in the MediaPlayer.
Is the way to do this correctly to encode by mp4 video file with 3 audio tracks (right left and narration) and then turn off the naration audio track with deselectTrack()?
Not clear to me from the documentation that MediaPlayer can handle more than 2 audio tracks.
If the audio tracks are limited to 2, would it make sense to run two media player simultaneously (synching them up with seekTo())when I want the narration track to play?
Thanks.
Sorry to burst your bubble, but...
1) You have a misunderstanding about what a "track" denotes. A track can have multiple channels (e.g., a stereo track has left and right channels). As I understand it, stereo is the extent of the Android AudioTrack implementation at present. I haven't yet checked if the OpenSL implementation is more extensive than the Java API.
2) Only 1 audio track can be selected at a time, so you wouldn't be able to have background and narration simultaneously in the way you were thinking.
3) Audio tracks can only be selected in the prepared state (i.e., not after playback has started). The documentation mentions this limitation is not ideal, so it will probably change in the future. If not for this problem, your goal could be accomplished with two audio tracks encoded in the stream, one with both background & narration, the other just background.
You will probably find it difficult to synchronize two MediaPlayers, but I haven't tried. Maybe this approach would be acceptable for your situation, although be forewarned the seekTo method isn't accurate. It depends on the encoding of the files.
Something I would try if I were you is to have two complete encoded videos, one with narration, the other without. Use two MediaPlayers and keep them both prepared. When you want to switch use seekTo to put the correct one at (or near) the desired location. That way you don't have to worry about synchronization. If the video is large, this method could use significantly more resources, though.
I want to write an app on Android to record snoring sounds of a sleeper and analyze it afterwards (i.e., not in real-time) for signs of a medical condition called obstructive sleep apnea.
The Android devices I've experimented with have voice recorders that produce a file format called .3ga. I want to programmatically read in the audio file and look at the amplitude for each individual time-sample. Then I can analyze that for patterns. Would this be easier if I converted this to a different format, e.g., MP3, and if so how can I do that programmatically?
I did a Google search on this and most of the hits seemed to be related to audio recording or playback which are unrelated to what I'm trying to do. I haven't coded anything yet because I don't know how to get started.
You are looking to do sample-based analysis on a raw audio signal, but the formats you mention are compressed. You will need to either deal with raw samples directly, or decompress the audio and then analyze.
Since you said you can do this work after-the-fact, why not upload to a server and analyze there?
I am trying to stream audio through a server. I have set up everything, and it's working fine with recording and playing back static audio, but when I am trying to stream an audio there is a delay on the playing side.
I did a Google search, but couldn't find the proper way of doing this. I am using AudioRecord & the Audiotrack Android media API for sending & receiving audio data. Can anybody tell me how to handle this delay?
I have added my code on GOOGLE GROUP to get clear picture.
I had tried in this way, holding 5 chunks of audio data in a buffer which comes through the server & playing back when it fills 5 chunks of data and again getting next 5 chunks of audio data and filling it like that it goes till 1024 bytes of data (it writes to the audiotrack & the play method is called).This too has a delay,any other solutions??
If you're really trying to do this unbuffered, make sure whatever playback tool you're using is trying to play it back without a buffer. You will be hard-pressed to not have a delay. Nothing on TV, radio, etc. is really 'live'--there is always some kind of delay. With internet streams, you're sending a large amount of data constantly. Even besides the time for it to travel, all this data has to be kept in a particular order and nobody wants choppy playback while the enduser's computer attempts playback. I've had flash players for major networks keep massive cache files on my computer while it's handling playback, but their players do not skip/wait to buffer/etc. (If you load up something and notice a few 100 MBs of extra memory being used, maybe even more during playback, that's what that is.)
You might be able to get away with a very small buffer (the standard in the past used to be 30-60 seconds and a lot of players still default to this) using VLC. I have been able to set its buffer very low but it is on incredibly low quality streams/videos. The big problem you have though I'd guess is your playback is setting the buffer and if your playback is set to 60 seconds buffer, it doesn't matter what you do serverside...the client end will wait until it has that much of a chunk and then begin playback.