I have a video taken from my mobile in portrait mode. Here is the dumped info about the video:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video.MOV':
Metadata:
major_brand : qt
minor_version : 0
compatible_brands: qt
creation_time : 2017-05-04 02:21:37
Duration: 00:00:06.91, start: 0.000023, bitrate: 4700 kb/s
Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 90 kb/s (default)
Metadata:
creation_time : 2017-05-04 02:21:37
handler_name : Core Media Data Handler
Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720, 4602 kb/s, 29.98 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
Metadata:
rotate : 90
creation_time : 2017-05-04 02:21:37
handler_name : Core Media Data Handler
encoder : H.264
Side data:
displaymatrix: rotation of -90.00 degrees
5.78 A-V: -0.028 fd= 1 aq= 14KB vq= 351KB sq= 0B f=0/0
I am using libav api to decode/encode my video. After encoding, I get the rotated version of the video by -90 degrees.
How can I stop decoder to prevent auto-rotation?
After a long time dealing with problems caused by display matrix side data, I came across the following solutions:
Copy the metadata and side data along with video stream. This code does the trick
AVStream *in_stream; //input stream
AVStream *out_stream; //output stream
....
if(in_stream->side_data!=NULL){
av_log(NULL, AV_LOG_ERROR, "side data size: %d , size: %d\n", in_stream->side_data->size, sizeof(uint8_t*));
if(av_stream_get_side_data(in_stream , AV_PKT_DATA_DISPLAYMATRIX, sd_size)!=NULL){
uint8_t* resp=(uint8_t*) av_mallocz(in_stream->side_data->size+
AV_INPUT_BUFFER_MIN_SIZE);
resp = av_stream_get_side_data(in_stream , AV_PKT_DATA_DISPLAYMATRIX, sd_size);
av_log(NULL, AV_LOG_DEBUG,"side data detected, size :%d vs %d, "
"nb_side_data %d, sizeof data %d,"
" sizeof resp %d\n",
*sd_size, in_stream->side_data->size ,in_stream->nb_side_data,
in_stream->side_data->size*sizeof(uint8_t*),sizeof(resp));
in_stream->side_data->data = (uint8_t*) av_mallocz(
in_stream->side_data->size*sizeof(uint8_t*)
);
hasRotation = true; /* it will be used for
something like ffmpeg does with noautorotate flag */
av_stream_add_side_data(out_stream, AV_PKT_DATA_DISPLAYMATRIX, resp, *sd_size);
}
}
The resulting video will have a display matrix, and some players will show them right.
Using simple filters As demonstrated above, one can detect the video is rotated. In my case the rotation is -90, so I use transpose=clock filter in initiating my filtergraph. Consider transoding example in ffmpeg 3.4.1. I change the code as follow to disable autorotate by -90 degrees.
static int init_filters(void) { const char *filter_spec; unsigned int i; int ret; filter_ctx = (FilteringContext*) av_malloc_array(ifmt_ctx->nb_streams, sizeof(*filter_ctx)); if (!filter_ctx) return AVERROR(ENOMEM); for (i = 0; i < ifmt_ctx->nb_streams; i++) { filter_ctx[i].buffersrc_ctx = NULL; filter_ctx[i].buffersink_ctx = NULL; filter_ctx[i].filter_graph = NULL; if (!(ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO || ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)) continue; if (ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) filter_spec = isRotated ?"transpose=clock":"null"; /* passthrough (dummy) filter for video */ else filter_spec = "anull"; /* passthrough (dummy) filter for audio */ ret = init_filter(&filter_ctx[i], stream_ctx[i].dec_ctx, stream_ctx[i].enc_ctx, filter_spec); if (ret) return ret; } return 0; }
Note that the encoder dimensions should also be swapped. It means:
enc_ctx->width = dec_ctx->height;
enc_ctx->height = enc_ctx->width;
I hope it would help others.
来源：https://stackoverflow.com/questions/44902474/how-to-disable-libav-autorotate-display-matrix