video interview questions
Top video frequently asked interview questions
I've seen plenty of info about how to stream video from the server to an android device, but not much about the other way, ala Qik. Could someone point me in the right direction here, or give me some advice on how to approach this?
Source: (StackOverflow)
I've built a web app that uses the HTML5 tag and JavaScript code that renders other content synchronized with the running video. It works great in desktop browsers: Firefox, Chrome, and Safari. On an iPhone or a DroidX, the native video player pops up and takes over the screen, thus obscuring the other dynamic content that I want to display simultaneously with the video.
Is there any way around this? If necessary, I'll figure out how to write native apps for both those platforms, but it would save me a ton of effort if I could just stick with HTML5/JavaScript.
Source: (StackOverflow)
1) CMTimeMake(1,10) means duration of 1 second and timescale of 10, or 10 frames per second. This means 1s duration of video with 10 frames?
2)
CMTime lastTime=CMTimeMake(1,10);
CMTime frameTime=CMTimeMake(1, 10);
CMTime currentTime=CMTimeAdd(lastTime, frameTime)
= (2, 10) ?
2 seconds of video and with 10 frames per second of the currentTime?
Source: (StackOverflow)
I have a set of video frames saved as images in a directory, and I'm trying to encode these to a good quality video, however every setting and every format I try produces very noticeable artifacts.
The basic command is this:
ffmpeg -r 25 -i %4d.png myvideo.mpg
and I've tried the minrate and maxrate flags. Any of {mpg, avi, mov, flv} formats will do.
Any suggestions for settings? Final file size is not an issue.
Source: (StackOverflow)
I want to use a video as a background instead of an image that automatically stretches to the whole screen (background).
I would also like to rotate videos and images.. so that there is a random video/image displayed in any order.
It would also be nice to know how to delay video playback, so that the video only plays once 30 seconds after the site loaded.
thx!
Source: (StackOverflow)
Does anyone know about any software that can convert video (avi, flv, whatever) to HTML5 supported ogg/ogv and mpeg4 formats?
I tried a few but I couldn't find anything that actually works.
Source: (StackOverflow)
Hey - I am using ffmpeg to tell me video info. Specifically:
ffmpeg -i video.ext
I get the output:
Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 704x576 [PAR 12:11 DAR 4:3], 9578 kb/s, 25 tbr, 90k tbn, 50 tbc
Does anyone know what tbr, tbn and tbc are exactly? I have seen speculation on the net but nothing definitive?
Thanks in advance.
Source: (StackOverflow)
According to:
http://developer.android.com/sdk/android-2.0-highlights.html
Android 2.0 should support the HTML5 video element. I haven't been able to get this to work using a Motorola Droid, and haven't been able to successfully view a video on any of the HTML5 video example pages out there. Since there currently isn't support for QuickTime or Flash, this is the only other thing I can think of for embedding mp4 video in a web page. Has anyone had any luck with this?
Source: (StackOverflow)
I am developing an App where I decode a video and replace certain frames and re-encode using MediaMuxer and MediaCodec. The App works if I do not replace any frames (except for 1080p videos as I explain below), but when I do, the frames after the replaced ones are pixelated and the video is choppy.
Also, when I try my app with 1920x1080 videos, I get a strange output, where the video is not showing anything, until I scroll to the beginning of the video, then the video starts showing up (but with the same problem mentioned before of pixalation after the edit.
Here is how I configure my encoder:
Video_format.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, interval);
Video_format.setInteger(MediaFormat.KEY_BIT_RATE, bitRate);
Video_format.setInteger(MediaFormat.KEY_FRAME_RATE, frameRate);
Video_format.setInteger(MediaFormat.KEY_MAX_INPUT_SIZE, 0);
int color_format=MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420SemiPlanar;
Video_format.setInteger(MediaFormat.KEY_COLOR_FORMAT, color_format);
encoder.configure(Video_format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
So to sum up, I have two problems:
1- Pixelated frames and choppy video after modified frames.
2- Corrupted 1920x1080 videos unless I scroll to the beginning.
Edit
Here is a sample 1080p video unedited, which gives a green screen when I play on VLC and plays incorrectly on the phone unless I scroll to start and now strangely working normally on YouTube, except for a green frame at the start
Here is a sample 720p video edited with also a green frame at the start and clear pixelation and lag after the edit
Here is the code I use to decode an re-encode:
do{
Bitmap b1;
if(edited_frames.containsKey(extractor.getSampleTime()))
b1=BitmapFactory.decodeFile(edited_frames.get(extractor.getSampleTime()));
else
b1=decode(extractor.getSampleTime(),Preview_width,Preview_Height);
if(b1==null) continue;
Bitmap b_scal=Bitmap.createScaledBitmap(b1, Preview_width, Preview_Height, false);
if(b_scal==null) continue;
encode(b_scal, encoder, muxer, videoTrackIndex);
lastTime=extractor.getSampleTime();
}while(extractor.advance());
The decode method:
private Bitmap decode(final long time,final int width,final int height){
MediaFormat newFormat = codec.getOutputFormat();
Bitmap b = null;
final int TIMEOUT_USEC = 10000;
ByteBuffer[] decoderInputBuffers = codec.getInputBuffers();
MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();
boolean outputDone = false;
boolean inputDone = false;
while (!outputDone) {
if (!inputDone) {
int inputBufIndex = codec.dequeueInputBuffer(TIMEOUT_USEC);
if (inputBufIndex >= 0) {
ByteBuffer inputBuf = decoderInputBuffers[inputBufIndex];
int chunkSize = extractor.readSampleData(inputBuf, 0);
if (chunkSize < 0) {
codec.queueInputBuffer(inputBufIndex, 0, 0, 0L, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
inputDone = true;
} else {
long presentationTimeUs = extractor.getSampleTime();
codec.queueInputBuffer(inputBufIndex, 0, chunkSize, presentationTimeUs, 0 );
}
inputBuf.clear();
decoderInputBuffers[inputBufIndex].clear();
} else {
}
}
ByteBuffer[] outputBuffers;
if (!outputDone) {
int decoderStatus = codec.dequeueOutputBuffer(info, TIMEOUT_USEC);
if (decoderStatus == MediaCodec.INFO_TRY_AGAIN_LATER) {
} else if (decoderStatus == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
outputBuffers = codec.getOutputBuffers();
} else if (decoderStatus == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
newFormat = codec.getOutputFormat();
} else if (decoderStatus < 0) {
} else {
if ((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
outputDone = true;
}
boolean doRender = (info.size != 0);
codec.releaseOutputBuffer(decoderStatus, false);
if (doRender) {
outputBuffers = codec.getOutputBuffers();
ByteBuffer buffer = outputBuffers[decoderStatus];
buffer = outputBuffers[decoderStatus];
outputDone = true;
byte[] outData = new byte[info.size];
buffer.get(outData);
buffer.clear();
outputBuffers[decoderStatus].clear();
try {
int colr_format=-1;
if(newFormat!=null && newFormat.getInteger(MediaFormat.KEY_COLOR_FORMAT)==21){
colr_format=ImageFormat.NV21;
}else if(newFormat!=null && newFormat.getInteger(MediaFormat.KEY_COLOR_FORMAT)!=21){
Toast.makeText(getApplicationContext(), "Unknown color format "+format.getInteger(MediaFormat.KEY_COLOR_FORMAT), Toast.LENGTH_LONG).show();
finish();
return null;
}
int[] arrrr=new int[format.getInteger(MediaFormat.KEY_WIDTH)* format.getInteger(MediaFormat.KEY_HEIGHT)];
YUV_NV21_TO_RGB(arrrr, outData, format.getInteger(MediaFormat.KEY_WIDTH), format.getInteger(MediaFormat.KEY_HEIGHT));
lastPresentationTimeUs = info.presentationTimeUs;
b = Bitmap.createBitmap(arrrr, format.getInteger(MediaFormat.KEY_WIDTH), format.getInteger(MediaFormat.KEY_HEIGHT), Bitmap.Config.ARGB_8888);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
return b;
}
And here is the encode method:
private void encode(Bitmap b, MediaCodec encoder, MediaMuxer muxer, int track_indx){
MediaCodec.BufferInfo enc_info = new MediaCodec.BufferInfo();
boolean enc_outputDone = false;
boolean enc_inputDone = false;
final int TIMEOUT_USEC = 10000;
ByteBuffer[] encoderInputBuffers = encoder.getInputBuffers();
ByteBuffer[] enc_outputBuffers = encoder.getOutputBuffers();
while (!enc_outputDone) {
if (!enc_inputDone) {
int inputBufIndex = encoder.dequeueInputBuffer(TIMEOUT_USEC);
if (inputBufIndex >= 0) {
ByteBuffer inputBuf = encoderInputBuffers[inputBufIndex];
int chunkSize = 0;
if(b==null){
}else{
int mWidth = b.getWidth();
int mHeight = b.getHeight();
byte [] yuv = new byte[mWidth*mHeight*3/2];
int [] argb = new int[mWidth * mHeight];
b.getPixels(argb, 0, mWidth, 0, 0, mWidth, mHeight);
encodeYUV420SP(yuv, argb, mWidth, mHeight);
b.recycle();
b=null;
inputBuf.put(yuv);
chunkSize = yuv.length;
}
if (chunkSize < 0) {
encoder.queueInputBuffer(inputBufIndex, 0, 0, 0L,
MediaCodec.BUFFER_FLAG_END_OF_STREAM);
} else {
long presentationTimeUs = extractor.getSampleTime();
Log.i("Encode","Encode Time: "+presentationTimeUs);
encoder.queueInputBuffer(inputBufIndex, 0, chunkSize, presentationTimeUs, 0);
inputBuf.clear();
encoderInputBuffers[inputBufIndex].clear();
enc_inputDone=true;
}
}
}
if (!enc_outputDone) {
int enc_decoderStatus = encoder.dequeueOutputBuffer(enc_info, TIMEOUT_USEC);
if (enc_decoderStatus == MediaCodec.INFO_TRY_AGAIN_LATER) {
} else if (enc_decoderStatus == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
enc_outputBuffers = encoder.getOutputBuffers();
} else if (enc_decoderStatus == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
MediaFormat newFormat = encoder.getOutputFormat();
} else if (enc_decoderStatus < 0) {
} else {
if ((enc_info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
enc_outputDone = true;
}
boolean enc_doRender = (enc_info.size != 0);
encoder.releaseOutputBuffer(enc_decoderStatus, false);
if (enc_doRender) {
enc_outputDone = true;
ByteBuffer enc_buffer = enc_outputBuffers[enc_decoderStatus];
try {
muxer.writeSampleData(track_indx, enc_buffer, enc_info);
} catch (Exception e) {
e.printStackTrace();
}
enc_buffer.clear();
enc_outputBuffers[enc_decoderStatus].clear();
}
}
}
}
Source: (StackOverflow)
Despite all the hype, in reality the HTML5 video tag has a bit of a problem. In order to use it and for it to be cross browser compatible, you have to include more than one format of the video. To target all supported browsers these formats are mp4 and ogg.
I was searching around for optimum settings for each format but unfortunately I couldn't find any. I'm using ffmpeg 0.6 which has the tagline "Works with HTML5". I'm no video expert so I was wondering if anyone could recommend decent settings for each format?
Source: (StackOverflow)
Can I use a <video> or <audio> tag to play a playlist, and to control them?
My goal is to know when a video/song has finished to play and take the next and change its volume.
Source: (StackOverflow)
i'm trying to build a video player, that works everywhere. so far i'd be going with:
<video>
<source src="video.mp4"></source>
<source src="video.ogv"></source>
<object data="flowplayer.swf" type="application/x-shockwave-flash">
<param name="movie" value="flowplayer.swf" />
<param name="flashvars" value='config={"clip":"video.mp4"}' />
</object>
</video>
(as seen on several sites, for example video for everybody)
so far, so good.
but now i also want some kind of playlist/menu along with the video player, from which i can select other videos. those should be opened within my player right away. so i will have to "dynamically change the source of the video" (as seen on dev.opera.com/articles/everything-you-need-to-know-html5-video-audio/ - section "Let's look at another movie") with javascript. let's forget about the flashplayer (and thus IE) part for the time being, i will try to deal with that later.
so my JS to change the <source> tags should be something like:
<script>
function loadAnotherVideo() {
var video = document.getElementsByTagName('video')[0];
var sources = video.getElementsByTagName('source');
sources[0].src = 'video2.mp4';
sources[1].src = 'video2.ogv';
video.load();
}
</script>
problem is, this doesnt work in all browsers. namely, firefox =O
there is a nice page, where you can observe the problem i'm having: http://www.w3.org/2010/05/video/mediaevents.html
as soon as i trigger the load() method (in firefox, mind you), the video player dies.
now i have found out that when i don't use multiple <source> tags, but instead just one src attribute within the <video> tag, the whole thing DOES work in firefox.
so my plan is to just use that src attribute and determine the appropriate file using the canPlayType() function.
am i doing it wrong somehow or complicating things??
Source: (StackOverflow)
I have been searching the web for some time for a solid FFmpeg wrapper for C#/.NET. But I have yet to come up with something useful. I have found the following three projects, but all of them apears to be dead in early alpha stage.
FFmpeg.NET
ffmpeg-sharp
FFLIB.NET
So my question is if anyone knows of a wrapper project that is more mature?
I am not looking for a full transcoding engine with job queues and more.
Just a simple wrapper so I do not have to make a command line call and then parse the console output, but can make method calls and use eventlisteners for progress.
And please feel free to mention any active projects, even if they are stil in the early stages.
Source: (StackOverflow)