FFMPEG x264 encoding on Android - error with lookahead

Question

I am using FFMPEG + x264 on Android to encode YUV420 frames to a video file. I use the following code on each frame to encode them:

avcodec_encode_video2(gVideoWriteCodecCtx, &packet, pCurrentFrame, &gotPacket);

On the first few calls, the frame buffer gets filled and nothing is encoded. When the first encoding happens, a call is made to x264_lookahead_get_frames. I can see there that my frame array is correctly populated, but the first item is NULL. As a consequence, in x264_weights_analyse the reference frame gotten as frames[p0] is NULL and I get an exception there.

slicetype.c, the first frame in "frames" is NULL

if( h->param.analyse.i_weighted_pred && b == p1 )
    {
        x264_emms();
        x264_weights_analyse( h, fenc, frames[p0], 1 );
        w = fenc->weight[0];
    }

And the exception happens there, ref is NULL

static void x264_weights_analyse( x264_t *h, x264_frame_t *fenc, x264_frame_t *ref, int b_lookahead )
    {
        int i_delta_index = fenc->i_frame - ref->i_frame - 1;

I surely am missing something as I am sure this encoder works for most people :) Does anyone have an idea why this first frame in the "frames" array is null?

Many thanks

Digging a bit more I noticed that in slicetype.c before this call there is a frames[0] = h->lookahead->last_nonb; This last_nonb has never been updated and is null. — tishu

tishu tishu · Accepted Answer · 2013-01-05T23:02:57

If that can help anyone, it looks like something weird in the library. Inverting these two lines in lookahead.c line236 made the job:

x264_stack_align( x264_slicetype_decide, h );
x264_lookahead_update_last_nonb( h, h->lookahead->next.list[0] );

to

x264_lookahead_update_last_nonb( h, h->lookahead->next.list[0] );
x264_stack_align( x264_slicetype_decide, h );

FFMPEG x264 encoding on Android - error with lookahead

1 Answers