Hi,
I am using libavcodec and libavformat to transcode WMV video files to AVI
using MPEG2. I can transcode the files fine when it comes to video only but
when I come to encode and multiplex the audio into the file I get the sound
playing around 500ms before the video when playing back the AVI.
A code snippet below shows what I am upto:
while(av_read_frame(pFormatCtx, &packet)>=0)
{
// Is this a packet from the video stream or audio stream?
if ( packet.stream_index == audioStream )
{
int data_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
int len = avcodec_decode_audio2( aCodecCtx, (int16_t*)this->samples,
&data_size,
packet.data, packet.size );
if ( data_size > 0 )
{
writeAudioFrame();
}
}
else if(packet.stream_index==videoStream)
{
// Decode video frame
avcodec_decode_video( pCodecCtx, pFrame, &frameFinished,
packet.data, packet.size);
if(frameFinished)
{
static struct SwsContext * img_convert_ctx = NULL;
if(img_convert_ctx == NULL)
{
int w = pCodecCtx->width;
int h = pCodecCtx->height;
img_convert_ctx = sws_getContext( w, h,
STREAM_PIX_FMT /* source */,
w, h, PIX_FMT_RGB32 /* dest */, SWS_BICUBIC,
NULL, NULL, NULL);
if(img_convert_ctx == NULL)
{
fprintf(stderr, "Cannot initialize the conversion context!\n");
}
}
sws_scale( img_convert_ctx, pFrame->data,
pFrame->linesize, 0,
pCodecCtx->height,
pFrameRGB->data, pFrameRGB->linesize);
/* compute current audio and video time */
if (audio_st)
audio_pts = (double)audio_st->pts.val * audio_st->time_base.num /
audio_st->time_base.den;
else
audio_pts = 0.0;
if (video_st)
video_pts = (double)video_st->pts.val * video_st->time_base.num /
video_st->time_base.den;
else
video_pts = 0.0;
if ((!audio_st /*|| audio_pts >= STREAM_DURATION*/) &&
(!video_st /*|| video_pts >= STREAM_DURATION*/))
break;
/* write interleaved audio and video frames */
if (!video_st || (video_st && audio_st && audio_pts < video_pts))
{
//writeAudioFrame();
}
else
{
if ( !writeVideoFrame( pFrameRGB ) )
{
printf( "Video frame not written" );
}
}
}
}
--
Andy Bell
CTO
J2K Video Limited
T: +44 (0)20 8133 2473
M: +34 685 130097
E: [email protected]
W: www.j2kvideo.com
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