[Libav-user] got_picture_ptr of avcodec_decode_video2 always returns 0 for a particular MTS file

[Simon Daniels]

Hello,

I've come across a particular MTS file that doesn't seem to want to be
decoded. I've decoded plenty of other MTS, M4V, and MOV files with my code
so something seems to be unique to this one. I can play the file just fine
too. Any idea what's going on here?

Here's the media info for the bad file:
General
ID                               : 0 (0x0)
Complete name                    : D:\Projects\Investigation\00793.MTS
Format                           : BDAV
Format/Info                      : Blu-ray Video
File size                        : 91.9 MiB
Duration                         : 34s 97ms
Overall bit rate                 : 22.6 Mbps
Maximum Overall bit rate         : 24.0 Mbps

Video
ID                               : 4113 (0x1011)
Menu ID                          : 1 (0x1)
Format                           : AVC
Format/Info                      : Advanced Video Codec
Format profile                   : High at L4.0
Format settings, CABAC           : No
Format settings, ReFrames        : 2 frames
Format settings, GOP             : M=1, N=28
Codec ID                         : 27
Duration                         : 33s 984ms
Bit rate mode                    : Variable
Bit rate                         : 21.4 Mbps
Maximum bit rate                 : 22.6 Mbps
Width                            : 1 920 pixels
Height                           : 1 080 pixels
Display aspect ratio             : 16:9
Frame rate                       : 29.970 fps
Color space                      : YUV
Chroma subsampling               : 4:2:0
Bit depth                        : 8 bits
Scan type                        : Interlaced
Scan order                       : Top Field First
Bits/(Pixel*Frame)               : 0.345
Stream size                      : 86.8 MiB (94%)

Audio
ID                               : 4352 (0x1100)
Menu ID                          : 1 (0x1)
Format                           : AC-3
Format/Info                      : Audio Coding 3
Mode extension                   : CM (complete main)
Codec ID                         : 129
Duration                         : 34s 16ms
Bit rate mode                    : Constant
Bit rate                         : 256 Kbps
Channel(s)                       : 2 channels
Channel positions                : Front: L R
Sampling rate                    : 48.0 KHz
Bit depth                        : 16 bits
Compression mode                 : Lossy
Delay relative to video          : -34ms
Stream size                      : 1.04 MiB (1%)

Text
ID                               : 4608 (0x1200)
Menu ID                          : 1 (0x1)
Format                           : PGS
Codec ID                         : 144
Duration                         : 33s 602ms
Delay relative to video          : -34ms



Here's a somewhat simplified version of my code. I use av_open_input_file,
av_find_stream_info, avcodec_find_decoder, and avcodec_open in my helper
functions.


    // Allocate video frame
    pFrame=avcodec_alloc_frame();

    // Allocate an AVFrame structure
    pFrameYUV=avcodec_alloc_frame();
    if(pFrameYUV==NULL)
    {
        return NULL;
    }

    // Determine required buffer size and allocate buffer
    numBytes=avpicture_get_size(PIX_FMT_YUV420P, width, height);
    buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));

    // Assign appropriate parts of buffer to image planes in pFrameYUV
    avpicture_fill((AVPicture *)pFrameYUV, buffer, PIX_FMT_YUV420P, width,
height);

    AVFormatContext* pFormatCtx;
    pFormatCtx = pHelper->FormatContextPointer();

    int videoStreamIndex = pHelper->VideoStreamIndex();
    int frameScanCount = 0;

    AVCodecContext* pCodecCtx;
    pCodecCtx = pHelper->CodecContextPointer();

    while (av_read_frame(pFormatCtx, &packet) >= 0)
    {


        // Is this a packet from the video stream?
        if (packet.stream_index == videoStreamIndex &&
            frameLocation++)
        {

            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrameYUV, &isFrameFinished,
&packet);

            *// FOR THIS VIDEO, **isFrameFinished **IS ALWAYS 0*
            if (isFrameFinished == 0)
            {
                pLog->Write("Frame %d not finished", frameLocation);
            }

            // Did we get a video frame?
            if (isFrameFinished) {

                // do some analysis on the pixels

            } // whether we successfully decoded the frame


        } // whether we were supposed to decode the frame

        av_free_packet(&packet);

    } // for each available frame

    //delete [] buffer;
    av_free(buffer);
    av_free(pFrame);

    // Free the YUV frame
    av_free(pFrameYUV);


Thanks!

Simon
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